Active Support is the Ruby on Rails component responsible for providing Ruby language extensions, utilities, and other transversal stuff.
It offers a richer bottom-line at the language level, targeted both at the development of Rails applications, and at the development of Ruby on Rails itself.
After reading this guide, you will know:
In order to have a near-zero default footprint, Active Support does not load anything by default. It is broken in small pieces so that you can load just what you need, and also has some convenience entry points to load related extensions in one shot, even everything.
Thus, after a simple require like:
require 'active_support'
objects do not even respond to blank?
. Let’s see how to load its definition.
The most lightweight way to get blank?
is to cherry-pick the file that defines it.
For every single method defined as a core extension this guide has a note that says where such a method is defined. In the case of blank?
the note reads:
NOTE: Defined in active_support/core_ext/object/blank.rb
.
That means that this single call is enough:
require 'active_support/core_ext/object/blank'
Active Support has been carefully revised so that cherry-picking a file loads only strictly needed dependencies, if any.
The next level is to simply load all extensions to Object
. As a rule of thumb, extensions to SomeClass
are available in one shot by loading active_support/core_ext/some_class
.
Thus, to load all extensions to Object
(including blank?
):
require 'active_support/core_ext/object'
You may prefer just to load all core extensions, there is a file for that:
require 'active_support/core_ext'
And finally, if you want to have all Active Support available just issue:
require 'active_support/all'
That does not even put the entire Active Support in memory upfront indeed, some stuff is configured via autoload
, so it is only loaded if used.
A Ruby on Rails application loads all Active Support unless config.active_support.bare
is true. In that case, the application will only load what the framework itself cherry-picks for its own needs, and can still cherry-pick itself at any granularity level, as explained in the previous section.
blank?
and present?
The following values are considered to be blank in a Rails application:
nil
and false
,
strings composed only of whitespace (see note below),
empty arrays and hashes, and
any other object that responds to empty?
and is empty.
INFO: The predicate for strings uses the Unicode-aware character class [:space:]
, so for example U+2029 (paragraph separator) is considered to be whitespace.
WARNING: Note that numbers are not mentioned. In particular, 0 and 0.0 are not blank.
For example, this method from ActionDispatch::Session::AbstractStore
uses blank?
for checking whether a session key is present:
def ensure_session_key! if @key.blank? raise ArgumentError, 'A key is required...' end end
The method present?
is equivalent to !blank?
. This example is taken from ActionDispatch::Http::Cache::Response
:
def set_conditional_cache_control! return if self["Cache-Control"].present? ... end
NOTE: Defined in active_support/core_ext/object/blank.rb
.
presence
The presence
method returns its receiver if present?
, and nil
otherwise. It is useful for idioms like this:
host = config[:host].presence || 'localhost'
NOTE: Defined in active_support/core_ext/object/blank.rb
.
duplicable?
A few fundamental objects in Ruby are singletons. For example, in the whole life of a program the integer 1 refers always to the same instance:
1.object_id # => 3 Math.cos(0).to_i.object_id # => 3
Hence, there’s no way these objects can be duplicated through dup
or clone
:
true.dup # => TypeError: can't dup TrueClass
Some numbers which are not singletons are not duplicable either:
0.0.clone # => allocator undefined for Float (2**1024).clone # => allocator undefined for Bignum
Active Support provides duplicable?
to programmatically query an object about this property:
"foo".duplicable? # => true "".duplicable? # => true 0.0.duplicable? # => false false.duplicable? # => false
By definition all objects are duplicable?
except nil
, false
, true
, symbols, numbers, class, and module objects.
WARNING: Any class can disallow duplication by removing dup
and clone
or raising exceptions from them. Thus only rescue
can tell whether a given arbitrary object is duplicable. duplicable?
depends on the hard-coded list above, but it is much faster than rescue
. Use it only if you know the hard-coded list is enough in your use case.
NOTE: Defined in active_support/core_ext/object/duplicable.rb
.
deep_dup
The deep_dup
method returns deep copy of a given object. Normally, when you dup
an object that contains other objects, ruby does not dup
them, so it creates a shallow copy of the object. If you have an array with a string, for example, it will look like this:
array = ['string'] duplicate = array.dup duplicate.push 'another-string' # the object was duplicated, so the element was added only to the duplicate array #=> ['string'] duplicate #=> ['string', 'another-string'] duplicate.first.gsub!('string', 'foo') # first element was not duplicated, it will be changed in both arrays array #=> ['foo'] duplicate #=> ['foo', 'another-string']
As you can see, after duplicating the Array
instance, we got another object, therefore we can modify it and the original object will stay unchanged. This is not true for array’s elements, however. Since dup
does not make deep copy, the string inside the array is still the same object.
If you need a deep copy of an object, you should use deep_dup
. Here is an example:
array = ['string'] duplicate = array.deep_dup duplicate.first.gsub!('string', 'foo') array #=> ['string'] duplicate #=> ['foo']
If the object is not duplicable, deep_dup
will just return it:
number = 1 duplicate = number.deep_dup number.object_id == duplicate.object_id # => true
NOTE: Defined in active_support/core_ext/object/deep_dup.rb
.
try
When you want to call a method on an object only if it is not nil
, the simplest way to achieve it is with conditional statements, adding unnecessary clutter. The alternative is to use try
. try
is like Object#send
except that it returns nil
if sent to nil
.
Here is an example:
# without try unless @number.nil? @number.next end # with try @number.try(:next)
Another example is this code from ActiveRecord::ConnectionAdapters::AbstractAdapter
where @logger
could be nil
. You can see that the code uses try
and avoids an unnecessary check.
def log_info(sql, name, ms) if @logger.try(:debug?) name = '%s (%.1fms)' % [name || 'SQL', ms] @logger.debug(format_log_entry(name, sql.squeeze(' '))) end end
try
can also be called without arguments but a block, which will only be executed if the object is not nil:
@person.try { |p| "#{p.first_name} #{p.last_name}" }
NOTE: Defined in active_support/core_ext/object/try.rb
.
class_eval(*args, &block)
You can evaluate code in the context of any object’s singleton class using class_eval
:
class Proc def bind(object) block, time = self, Time.current object.class_eval do method_name = "__bind_#{time.to_i}_#{time.usec}" define_method(method_name, &block) method = instance_method(method_name) remove_method(method_name) method end.bind(object) end end
NOTE: Defined in active_support/core_ext/kernel/singleton_class.rb
.
acts_like?(duck)
The method acts_like?
provides a way to check whether some class acts like some other class based on a simple convention: a class that provides the same interface as String
defines
def acts_like_string? end
which is only a marker, its body or return value are irrelevant. Then, client code can query for duck-type-safeness this way:
some_klass.acts_like?(:string)
Rails has classes that act like Date
or Time
and follow this contract.
NOTE: Defined in active_support/core_ext/object/acts_like.rb
.
to_param
All objects in Rails respond to the method to_param
, which is meant to return something that represents them as values in a query string, or as URL fragments.
By default to_param
just calls to_s
:
7.to_param # => "7"
The return value of to_param
should not be escaped:
"Tom & Jerry".to_param # => "Tom & Jerry"
Several classes in Rails overwrite this method.
For example nil
, true
, and false
return themselves. Array#to_param
calls to_param
on the elements and joins the result with “/”:
[0, true, String].to_param # => "0/true/String"
Notably, the Rails routing system calls to_param
on models to get a value for the :id
placeholder. ActiveRecord::Base#to_param
returns the id
of a model, but you can redefine that method in your models. For example, given
class User def to_param "#{id}-#{name.parameterize}" end end
we get:
user_path(@user) # => "/users/357-john-smith"
WARNING. Controllers need to be aware of any redefinition of to_param
because when a request like that comes in “357-john-smith” is the value of params[:id]
.
NOTE: Defined in active_support/core_ext/object/to_param.rb
.
to_query
Except for hashes, given an unescaped key
this method constructs the part of a query string that would map such key to what to_param
returns. For example, given
class User def to_param "#{id}-#{name.parameterize}" end end
we get:
current_user.to_query('user') # => user=357-john-smith
This method escapes whatever is needed, both for the key and the value:
account.to_query('company[name]') # => "company%5Bname%5D=Johnson+%26+Johnson"
so its output is ready to be used in a query string.
Arrays return the result of applying to_query
to each element with _key_[]
as key, and join the result with “&”:
[3.4, -45.6].to_query('sample') # => "sample%5B%5D=3.4&sample%5B%5D=-45.6"
Hashes also respond to to_query
but with a different signature. If no argument is passed a call generates a sorted series of key/value assignments calling to_query(key)
on its values. Then it joins the result with “&”:
{c: 3, b: 2, a: 1}.to_query # => "a=1&b=2&c=3"
The method Hash#to_query
accepts an optional namespace for the keys:
{id: 89, name: "John Smith"}.to_query('user') # => "user%5Bid%5D=89&user%5Bname%5D=John+Smith"
NOTE: Defined in active_support/core_ext/object/to_query.rb
.
with_options
The method with_options
provides a way to factor out common options in a series of method calls.
Given a default options hash, with_options
yields a proxy object to a block. Within the block, methods called on the proxy are forwarded to the receiver with their options merged. For example, you get rid of the duplication in:
class Account < ActiveRecord::Base has_many :customers, dependent: :destroy has_many :products, dependent: :destroy has_many :invoices, dependent: :destroy has_many :expenses, dependent: :destroy end
this way:
class Account < ActiveRecord::Base with_options dependent: :destroy do |assoc| assoc.has_many :customers assoc.has_many :products assoc.has_many :invoices assoc.has_many :expenses end end
That idiom may convey grouping to the reader as well. For example, say you want to send a newsletter whose language depends on the user. Somewhere in the mailer you could group locale-dependent bits like this:
I18n.with_options locale: user.locale, scope: "newsletter" do |i18n| subject i18n.t :subject body i18n.t :body, user_name: user.name end
TIP: Since with_options
forwards calls to its receiver they can be nested. Each nesting level will merge inherited defaults in addition to their own.
NOTE: Defined in active_support/core_ext/object/with_options.rb
.
Active Support provides several methods to ease access to instance variables.
instance_values
The method instance_values
returns a hash that maps instance variable names without “@” to their
corresponding values. Keys are strings:
class C def initialize(x, y) @x, @y = x, y end end C.new(0, 1).instance_values # => {"x" => 0, "y" => 1}
NOTE: Defined in active_support/core_ext/object/instance_variables.rb
.
The methods silence_warnings
and enable_warnings
change the value of $VERBOSE
accordingly for the duration of their block, and reset it afterwards:
silence_warnings { Object.const_set "RAILS_DEFAULT_LOGGER", logger }
You can silence any stream while a block runs with silence_stream
:
silence_stream(STDOUT) do # STDOUT is silent here end
The quietly
method addresses the common use case where you want to silence STDOUT and STDERR, even in subprocesses:
quietly { system 'bundle install' }
For example, the railties test suite uses that one in a few places to prevent command messages from being echoed intermixed with the progress status.
Silencing exceptions is also possible with suppress
. This method receives an arbitrary number of exception classes. If an exception is raised during the execution of the block and is kind_of?
any of the arguments, suppress
captures it and returns silently. Otherwise the exception is reraised:
# If the user is locked the increment is lost, no big deal. suppress(ActiveRecord::StaleObjectError) do current_user.increment! :visits end
NOTE: Defined in active_support/core_ext/kernel/reporting.rb
.
in?
The predicate in?
tests if an object is included in another object. An ArgumentError
exception will be raised if the argument passed does not respond to include?
.
Examples of in?
:
1.in?([1,2]) # => true "lo".in?("hello") # => true 25.in?(30..50) # => false 1.in?(1) # => ArgumentError
NOTE: Defined in active_support/core_ext/object/inclusion.rb
.
Module
alias_method_chain
Using plain Ruby you can wrap methods with other methods, that’s called alias chaining.
For example, let’s say you’d like params to be strings in functional tests, as they are in real requests, but still want the convenience of assigning integers and other kind of values. To accomplish that you could wrap ActionController::TestCase#process
this way in test/test_helper.rb
:
ActionController::TestCase.class_eval do # save a reference to the original process method alias_method :original_process, :process # now redefine process and delegate to original_process def process(action, params=nil, session=nil, flash=nil, http_method='GET') params = Hash[*params.map {|k, v| [k, v.to_s]}.flatten] original_process(action, params, session, flash, http_method) end end
That’s the method get
, post
, etc., delegate the work to.
That technique has a risk, it could be the case that :original_process
was taken. To try to avoid collisions people choose some label that characterizes what the chaining is about:
ActionController::TestCase.class_eval do def process_with_stringified_params(...) params = Hash[*params.map {|k, v| [k, v.to_s]}.flatten] process_without_stringified_params(action, params, session, flash, http_method) end alias_method :process_without_stringified_params, :process alias_method :process, :process_with_stringified_params end
The method alias_method_chain
provides a shortcut for that pattern:
ActionController::TestCase.class_eval do def process_with_stringified_params(...) params = Hash[*params.map {|k, v| [k, v.to_s]}.flatten] process_without_stringified_params(action, params, session, flash, http_method) end alias_method_chain :process, :stringified_params end
Rails uses alias_method_chain
all over the code base. For example validations are added to ActiveRecord::Base#save
by wrapping the method that way in a separate module specialized in validations.
NOTE: Defined in active_support/core_ext/module/aliasing.rb
.
alias_attribute
Model attributes have a reader, a writer, and a predicate. You can alias a model attribute having the corresponding three methods defined for you in one shot. As in other aliasing methods, the new name is the first argument, and the old name is the second (my mnemonic is they go in the same order as if you did an assignment):
class User < ActiveRecord::Base # let me refer to the email column as "login", # possibly meaningful for authentication code alias_attribute :login, :email end
NOTE: Defined in active_support/core_ext/module/aliasing.rb
.
When you are defining an attribute in a class that is meant to be subclassed, name collisions are a risk. That’s remarkably important for libraries.
Active Support defines the macros attr_internal_reader
, attr_internal_writer
, and attr_internal_accessor
. They behave like their Ruby built-in attr_*
counterparts, except they name the underlying instance variable in a way that makes collisions less likely.
The macro attr_internal
is a synonym for attr_internal_accessor
:
# library class ThirdPartyLibrary::Crawler attr_internal :log_level end # client code class MyCrawler < ThirdPartyLibrary::Crawler attr_accessor :log_level end
In the previous example it could be the case that :log_level
does not belong to the public interface of the library and it is only used for development. The client code, unaware of the potential conflict, subclasses and defines its own :log_level
. Thanks to attr_internal
there’s no collision.
By default the internal instance variable is named with a leading underscore, @_log_level
in the example above. That’s configurable via Module.attr_internal_naming_format
though, you can pass any sprintf
-like format string with a leading @
and a %s
somewhere, which is where the name will be placed. The default is "@_%s"
.
Rails uses internal attributes in a few spots, for examples for views:
module ActionView class Base attr_internal :captures attr_internal :request, :layout attr_internal :controller, :template end end
NOTE: Defined in active_support/core_ext/module/attr_internal.rb
.
The macros mattr_reader
, mattr_writer
, and mattr_accessor
are analogous to the cattr_*
macros defined for class. Check Class Attributes.
For example, the dependencies mechanism uses them:
module ActiveSupport module Dependencies mattr_accessor :warnings_on_first_load mattr_accessor :history mattr_accessor :loaded mattr_accessor :mechanism mattr_accessor :load_paths mattr_accessor :load_once_paths mattr_accessor :autoloaded_constants mattr_accessor :explicitly_unloadable_constants mattr_accessor :logger mattr_accessor :log_activity mattr_accessor :constant_watch_stack mattr_accessor :constant_watch_stack_mutex end end
NOTE: Defined in active_support/core_ext/module/attribute_accessors.rb
.
parent
The parent
method on a nested named module returns the module that contains its corresponding constant:
module X module Y module Z end end end M = X::Y::Z X::Y::Z.parent # => X::Y M.parent # => X::Y
If the module is anonymous or belongs to the top-level, parent
returns Object
.
WARNING: Note that in that case parent_name
returns nil
.
NOTE: Defined in active_support/core_ext/module/introspection.rb
.
parent_name
The parent_name
method on a nested named module returns the fully-qualified name of the module that contains its corresponding constant:
module X module Y module Z end end end M = X::Y::Z X::Y::Z.parent_name # => "X::Y" M.parent_name # => "X::Y"
For top-level or anonymous modules parent_name
returns nil
.
WARNING: Note that in that case parent
returns Object
.
NOTE: Defined in active_support/core_ext/module/introspection.rb
.
parents
The method parents
calls parent
on the receiver and upwards until Object
is reached. The chain is returned in an array, from bottom to top:
module X module Y module Z end end end M = X::Y::Z X::Y::Z.parents # => [X::Y, X, Object] M.parents # => [X::Y, X, Object]
NOTE: Defined in active_support/core_ext/module/introspection.rb
.
The method local_constants
returns the names of the constants that have been
defined in the receiver module:
module X X1 = 1 X2 = 2 module Y Y1 = :y1 X1 = :overrides_X1_above end end X.local_constants # => [:X1, :X2, :Y] X::Y.local_constants # => [:Y1, :X1]
The names are returned as symbols. (The deprecated method local_constant_names
returns strings.)
NOTE: Defined in active_support/core_ext/module/introspection.rb
.
The standard methods const_defined?
, const_get
, and const_set
accept
bare constant names. Active Support extends this API to be able to pass
relative qualified constant names.
The new methods are qualified_const_defined?
, qualified_const_get
, and
qualified_const_set
. Their arguments are assumed to be qualified constant
names relative to their receiver:
Object.qualified_const_defined?("Math::PI") # => true Object.qualified_const_get("Math::PI") # => 3.141592653589793 Object.qualified_const_set("Math::Phi", 1.618034) # => 1.618034
Arguments may be bare constant names:
Math.qualified_const_get("E") # => 2.718281828459045
These methods are analogous to their builtin counterparts. In particular,
qualified_constant_defined?
accepts an optional second argument to be
able to say whether you want the predicate to look in the ancestors.
This flag is taken into account for each constant in the expression while
walking down the path.
For example, given
module M X = 1 end module N class C include M end end
qualified_const_defined?
behaves this way:
N.qualified_const_defined?("C::X", false) # => false N.qualified_const_defined?("C::X", true) # => true N.qualified_const_defined?("C::X") # => true
As the last example implies, the second argument defaults to true,
as in const_defined?
.
For coherence with the builtin methods only relative paths are accepted.
Absolute qualified constant names like ::Math::PI
raise NameError
.
NOTE: Defined in active_support/core_ext/module/qualified_const.rb
.
A named module is reachable if it is stored in its corresponding constant. It means you can reach the module object via the constant.
That is what ordinarily happens, if a module is called “M”, the M
constant exists and holds it:
module M end M.reachable? # => true
But since constants and modules are indeed kind of decoupled, module objects can become unreachable:
module M end orphan = Object.send(:remove_const, :M) # The module object is orphan now but it still has a name. orphan.name # => "M" # You cannot reach it via the constant M because it does not even exist. orphan.reachable? # => false # Let's define a module called "M" again. module M end # The constant M exists now again, and it stores a module # object called "M", but it is a new instance. orphan.reachable? # => false
NOTE: Defined in active_support/core_ext/module/reachable.rb
.
A module may or may not have a name:
module M end M.name # => "M" N = Module.new N.name # => "N" Module.new.name # => nil
You can check whether a module has a name with the predicate anonymous?
:
module M end M.anonymous? # => false Module.new.anonymous? # => true
Note that being unreachable does not imply being anonymous:
module M end m = Object.send(:remove_const, :M) m.reachable? # => false m.anonymous? # => false
though an anonymous module is unreachable by definition.
NOTE: Defined in active_support/core_ext/module/anonymous.rb
.
The macro delegate
offers an easy way to forward methods.
Let’s imagine that users in some application have login information in the User
model but name and other data in a separate Profile
model:
class User < ActiveRecord::Base has_one :profile end
With that configuration you get a user’s name via his profile, user.profile.name
, but it could be handy to still be able to access such attribute directly:
class User < ActiveRecord::Base has_one :profile def name profile.name end end
That is what delegate
does for you:
class User < ActiveRecord::Base has_one :profile delegate :name, to: :profile end
It is shorter, and the intention more obvious.
The method must be public in the target.
The delegate
macro accepts several methods:
delegate :name, :age, :address, :twitter, to: :profile
When interpolated into a string, the :to
option should become an expression that evaluates to the object the method is delegated to. Typically a string or symbol. Such an expression is evaluated in the context of the receiver:
# delegates to the Rails constant delegate :logger, to: :Rails # delegates to the receiver's class delegate :table_name, to: :class
WARNING: If the :prefix
option is true
this is less generic, see below.
By default, if the delegation raises NoMethodError
and the target is nil
the exception is propagated. You can ask that nil
is returned instead with the :allow_nil
option:
delegate :name, to: :profile, allow_nil: true
With :allow_nil
the call user.name
returns nil
if the user has no profile.
The option :prefix
adds a prefix to the name of the generated method. This may be handy for example to get a better name:
delegate :street, to: :address, prefix: true
The previous example generates address_street
rather than street
.
WARNING: Since in this case the name of the generated method is composed of the target object and target method names, the :to
option must be a method name.
A custom prefix may also be configured:
delegate :size, to: :attachment, prefix: :avatar
In the previous example the macro generates avatar_size
rather than size
.
NOTE: Defined in active_support/core_ext/module/delegation.rb
There are cases where you need to define a method with define_method
, but don’t know whether a method with that name already exists. If it does, a warning is issued if they are enabled. No big deal, but not clean either.
The method redefine_method
prevents such a potential warning, removing the existing method before if needed. Rails uses it in a few places, for instance when it generates an association’s API:
redefine_method("#{reflection.name}=") do |new_value| association = association_instance_get(reflection.name) if association.nil? || association.target != new_value association = association_proxy_class.new(self, reflection) end association.replace(new_value) association_instance_set(reflection.name, new_value.nil? ? nil : association) end
NOTE: Defined in active_support/core_ext/module/remove_method.rb
Class
class_attribute
The method class_attribute
declares one or more inheritable class attributes that can be overridden at any level down the hierarchy.
class A class_attribute :x end class B < A; end class C < B; end A.x = :a B.x # => :a C.x # => :a B.x = :b A.x # => :a C.x # => :b C.x = :c A.x # => :a B.x # => :b
For example ActionMailer::Base
defines:
class_attribute :default_params self.default_params = { mime_version: "1.0", charset: "UTF-8", content_type: "text/plain", parts_order: [ "text/plain", "text/enriched", "text/html" ] }.freeze
They can be also accessed and overridden at the instance level.
A.x = 1 a1 = A.new a2 = A.new a2.x = 2 a1.x # => 1, comes from A a2.x # => 2, overridden in a2
The generation of the writer instance method can be prevented by setting the option :instance_writer
to false
.
module ActiveRecord class Base class_attribute :table_name_prefix, instance_writer: false self.table_name_prefix = "" end end
A model may find that option useful as a way to prevent mass-assignment from setting the attribute.
The generation of the reader instance method can be prevented by setting the option :instance_reader
to false
.
class A class_attribute :x, instance_reader: false end A.new.x = 1 # NoMethodError
For convenience class_attribute
also defines an instance predicate which is the double negation of what the instance reader returns. In the examples above it would be called x?
.
When :instance_reader
is false
, the instance predicate returns a NoMethodError
just like the reader method.
If you do not want the instance predicate, pass instance_predicate: false
and it will not be defined.
NOTE: Defined in active_support/core_ext/class/attribute.rb
cattr_reader
, cattr_writer
, and cattr_accessor
The macros cattr_reader
, cattr_writer
, and cattr_accessor
are analogous to their attr_*
counterparts but for classes. They initialize a class variable to nil
unless it already exists, and generate the corresponding class methods to access it:
class MysqlAdapter < AbstractAdapter # Generates class methods to access @@emulate_booleans. cattr_accessor :emulate_booleans self.emulate_booleans = true end
Instance methods are created as well for convenience, they are just proxies to the class attribute. So, instances can change the class attribute, but cannot override it as it happens with class_attribute
(see above). For example given
module ActionView class Base cattr_accessor :field_error_proc @@field_error_proc = Proc.new{ ... } end end
we can access field_error_proc
in views.
The generation of the reader instance method can be prevented by setting :instance_reader
to false
and the generation of the writer instance method can be prevented by setting :instance_writer
to false
. Generation of both methods can be prevented by setting :instance_accessor
to false
. In all cases, the value must be exactly false
and not any false value.
module A class B # No first_name instance reader is generated. cattr_accessor :first_name, instance_reader: false # No last_name= instance writer is generated. cattr_accessor :last_name, instance_writer: false # No surname instance reader or surname= writer is generated. cattr_accessor :surname, instance_accessor: false end end
A model may find it useful to set :instance_accessor
to false
as a way to prevent mass-assignment from setting the attribute.
NOTE: Defined in active_support/core_ext/class/attribute_accessors.rb
.
subclasses
The subclasses
method returns the subclasses of the receiver:
class C; end C.subclasses # => [] class B < C; end C.subclasses # => [B] class A < B; end C.subclasses # => [B] class D < C; end C.subclasses # => [B, D]
The order in which these classes are returned is unspecified.
NOTE: Defined in active_support/core_ext/class/subclasses.rb
.
descendants
The descendants
method returns all classes that are <
than its receiver:
class C; end C.descendants # => [] class B < C; end C.descendants # => [B] class A < B; end C.descendants # => [B, A] class D < C; end C.descendants # => [B, A, D]
The order in which these classes are returned is unspecified.
NOTE: Defined in active_support/core_ext/class/subclasses.rb
.
String
Inserting data into HTML templates needs extra care. For example, you can’t just interpolate @review.title
verbatim into an HTML page. For one thing, if the review title is “Flanagan & Matz rules!” the output won’t be well-formed because an ampersand has to be escaped as “&”. What’s more, depending on the application, that may be a big security hole because users can inject malicious HTML setting a hand-crafted review title. Check out the section about cross-site scripting in the Security guide for further information about the risks.
Active Support has the concept of (html) safe strings. A safe string is one that is marked as being insertable into HTML as is. It is trusted, no matter whether it has been escaped or not.
Strings are considered to be unsafe by default:
"".html_safe? # => false
You can obtain a safe string from a given one with the html_safe
method:
s = "".html_safe s.html_safe? # => true
It is important to understand that html_safe
performs no escaping whatsoever, it is just an assertion:
s = "<script>...</script>".html_safe s.html_safe? # => true s # => "<script>...</script>"
It is your responsibility to ensure calling html_safe
on a particular string is fine.
If you append onto a safe string, either in-place with concat
/<<
, or with +
, the result is a safe string. Unsafe arguments are escaped:
"".html_safe + "<" # => "<"
Safe arguments are directly appended:
"".html_safe + "<".html_safe # => "<"
These methods should not be used in ordinary views. Unsafe values are automatically escaped:
<%= @review.title %> <%# fine, escaped if needed %>
To insert something verbatim use the raw
helper rather than calling html_safe
:
<%= raw @cms.current_template %> <%# inserts @cms.current_template as is %>
or, equivalently, use <%==
:
<%== @cms.current_template %> <%# inserts @cms.current_template as is %>
The raw
helper calls html_safe
for you:
def raw(stringish) stringish.to_s.html_safe end
NOTE: Defined in active_support/core_ext/string/output_safety.rb
.
As a rule of thumb, except perhaps for concatenation as explained above, any method that may change a string gives you an unsafe string. These are downcase
, gsub
, strip
, chomp
, underscore
, etc.
In the case of in-place transformations like gsub!
the receiver itself becomes unsafe.
INFO: The safety bit is lost always, no matter whether the transformation actually changed something.
Calling to_s
on a safe string returns a safe string, but coercion with to_str
returns an unsafe string.
Calling dup
or clone
on safe strings yields safe strings.
squish
The method squish
strips leading and trailing whitespace, and substitutes runs of whitespace with a single space each:
" \n foo\n\r \t bar \n".squish # => "foo bar"
There’s also the destructive version String#squish!
.
Note that it handles both ASCII and Unicode whitespace like mongolian vowel separator (U+180E).
NOTE: Defined in active_support/core_ext/string/filters.rb
.
truncate
The method truncate
returns a copy of its receiver truncated after a given length
:
"Oh dear! Oh dear! I shall be late!".truncate(20) # => "Oh dear! Oh dear!..."
Ellipsis can be customized with the :omission
option:
"Oh dear! Oh dear! I shall be late!".truncate(20, omission: '…') # => "Oh dear! Oh …"
Note in particular that truncation takes into account the length of the omission string.
Pass a :separator
to truncate the string at a natural break:
"Oh dear! Oh dear! I shall be late!".truncate(18) # => "Oh dear! Oh dea..." "Oh dear! Oh dear! I shall be late!".truncate(18, separator: ' ') # => "Oh dear! Oh..."
The option :separator
can be a regexp:
"Oh dear! Oh dear! I shall be late!".truncate(18, separator: /\s/) # => "Oh dear! Oh..."
In above examples “dear” gets cut first, but then :separator
prevents it.
NOTE: Defined in active_support/core_ext/string/filters.rb
.
inquiry
The inquiry
method converts a string into a StringInquirer
object making equality checks prettier.
"production".inquiry.production? # => true "active".inquiry.inactive? # => false
starts_with?
and ends_with?
Active Support defines 3rd person aliases of String#start_with?
and String#end_with?
:
"foo".starts_with?("f") # => true "foo".ends_with?("o") # => true
NOTE: Defined in active_support/core_ext/string/starts_ends_with.rb
.
strip_heredoc
The method strip_heredoc
strips indentation in heredocs.
For example in
if options[:usage] puts <<-USAGE.strip_heredoc This command does such and such. Supported options are: -h This message ... USAGE end
the user would see the usage message aligned against the left margin.
Technically, it looks for the least indented line in the whole string, and removes that amount of leading whitespace.
NOTE: Defined in active_support/core_ext/string/strip.rb
.
indent
Indents the lines in the receiver:
<<EOS.indent(2) def some_method some_code end EOS # => def some_method some_code end
The second argument, indent_string
, specifies which indent string to use. The default is nil
, which tells the method to make an educated guess peeking at the first indented line, and fallback to a space if there is none.
" foo".indent(2) # => " foo" "foo\n\t\tbar".indent(2) # => "\t\tfoo\n\t\t\t\tbar" "foo".indent(2, "\t") # => "\t\tfoo"
While indent_string
is typically one space or tab, it may be any string.
The third argument, indent_empty_lines
, is a flag that says whether empty lines should be indented. Default is false.
"foo\n\nbar".indent(2) # => " foo\n\n bar" "foo\n\nbar".indent(2, nil, true) # => " foo\n \n bar"
The indent!
method performs indentation in-place.
at(position)
Returns the character of the string at position position
:
"hello".at(0) # => "h" "hello".at(4) # => "o" "hello".at(-1) # => "o" "hello".at(10) # => nil
NOTE: Defined in active_support/core_ext/string/access.rb
.
from(position)
Returns the substring of the string starting at position position
:
"hello".from(0) # => "hello" "hello".from(2) # => "llo" "hello".from(-2) # => "lo" "hello".from(10) # => "" if < 1.9, nil in 1.9
NOTE: Defined in active_support/core_ext/string/access.rb
.
to(position)
Returns the substring of the string up to position position
:
"hello".to(0) # => "h" "hello".to(2) # => "hel" "hello".to(-2) # => "hell" "hello".to(10) # => "hello"
NOTE: Defined in active_support/core_ext/string/access.rb
.
first(limit = 1)
The call str.first(n)
is equivalent to str.to(n-1)
if n
> 0, and returns an empty string for n
== 0.
NOTE: Defined in active_support/core_ext/string/access.rb
.
last(limit = 1)
The call str.last(n)
is equivalent to str.from(-n)
if n
> 0, and returns an empty string for n
== 0.
NOTE: Defined in active_support/core_ext/string/access.rb
.
pluralize
The method pluralize
returns the plural of its receiver:
"table".pluralize # => "tables" "ruby".pluralize # => "rubies" "equipment".pluralize # => "equipment"
As the previous example shows, Active Support knows some irregular plurals and uncountable nouns. Built-in rules can be extended in config/initializers/inflections.rb
. That file is generated by the rails
command and has instructions in comments.
pluralize
can also take an optional count
parameter. If count == 1
the singular form will be returned. For any other value of count
the plural form will be returned:
"dude".pluralize(0) # => "dudes" "dude".pluralize(1) # => "dude" "dude".pluralize(2) # => "dudes"
Active Record uses this method to compute the default table name that corresponds to a model:
# active_record/model_schema.rb def undecorated_table_name(class_name = base_class.name) table_name = class_name.to_s.demodulize.underscore pluralize_table_names ? table_name.pluralize : table_name end
NOTE: Defined in active_support/core_ext/string/inflections.rb
.
singularize
The inverse of pluralize
:
"tables".singularize # => "table" "rubies".singularize # => "ruby" "equipment".singularize # => "equipment"
Associations compute the name of the corresponding default associated class using this method:
# active_record/reflection.rb def derive_class_name class_name = name.to_s.camelize class_name = class_name.singularize if collection? class_name end
NOTE: Defined in active_support/core_ext/string/inflections.rb
.
camelize
The method camelize
returns its receiver in camel case:
"product".camelize # => "Product" "admin_user".camelize # => "AdminUser"
As a rule of thumb you can think of this method as the one that transforms paths into Ruby class or module names, where slashes separate namespaces:
"backoffice/session".camelize # => "Backoffice::Session"
For example, Action Pack uses this method to load the class that provides a certain session store:
# action_controller/metal/session_management.rb def session_store=(store) @@session_store = store.is_a?(Symbol) ? ActionDispatch::Session.const_get(store.to_s.camelize) : store end
camelize
accepts an optional argument, it can be :upper
(default), or :lower
. With the latter the first letter becomes lowercase:
"visual_effect".camelize(:lower) # => "visualEffect"
That may be handy to compute method names in a language that follows that convention, for example JavaScript.
INFO: As a rule of thumb you can think of camelize
as the inverse of underscore
, though there are cases where that does not hold: "SSLError".underscore.camelize
gives back "SslError"
. To support cases such as this, Active Support allows you to specify acronyms in config/initializers/inflections.rb
:
ActiveSupport::Inflector.inflections do |inflect| inflect.acronym 'SSL' end "SSLError".underscore.camelize #=> "SSLError"
camelize
is aliased to camelcase
.
NOTE: Defined in active_support/core_ext/string/inflections.rb
.
underscore
The method underscore
goes the other way around, from camel case to paths:
"Product".underscore # => "product" "AdminUser".underscore # => "admin_user"
Also converts “::” back to “/”:
"Backoffice::Session".underscore # => "backoffice/session"
and understands strings that start with lowercase:
"visualEffect".underscore # => "visual_effect"
underscore
accepts no argument though.
Rails class and module autoloading uses underscore
to infer the relative path without extension of a file that would define a given missing constant:
# active_support/dependencies.rb def load_missing_constant(from_mod, const_name) ... qualified_name = qualified_name_for from_mod, const_name path_suffix = qualified_name.underscore ... end
INFO: As a rule of thumb you can think of underscore
as the inverse of camelize
, though there are cases where that does not hold. For example, "SSLError".underscore.camelize
gives back "SslError"
.
NOTE: Defined in active_support/core_ext/string/inflections.rb
.
titleize
The method titleize
capitalizes the words in the receiver:
"alice in wonderland".titleize # => "Alice In Wonderland" "fermat's enigma".titleize # => "Fermat's Enigma"
titleize
is aliased to titlecase
.
NOTE: Defined in active_support/core_ext/string/inflections.rb
.
dasherize
The method dasherize
replaces the underscores in the receiver with dashes:
"name".dasherize # => "name" "contact_data".dasherize # => "contact-data"
The XML serializer of models uses this method to dasherize node names:
# active_model/serializers/xml.rb def reformat_name(name) name = name.camelize if camelize? dasherize? ? name.dasherize : name end
NOTE: Defined in active_support/core_ext/string/inflections.rb
.
demodulize
Given a string with a qualified constant name, demodulize
returns the very constant name, that is, the rightmost part of it:
"Product".demodulize # => "Product" "Backoffice::UsersController".demodulize # => "UsersController" "Admin::Hotel::ReservationUtils".demodulize # => "ReservationUtils"
Active Record for example uses this method to compute the name of a counter cache column:
# active_record/reflection.rb def counter_cache_column if options[:counter_cache] == true "#{active_record.name.demodulize.underscore.pluralize}_count" elsif options[:counter_cache] options[:counter_cache] end end
NOTE: Defined in active_support/core_ext/string/inflections.rb
.
deconstantize
Given a string with a qualified constant reference expression, deconstantize
removes the rightmost segment, generally leaving the name of the constant’s container:
"Product".deconstantize # => "" "Backoffice::UsersController".deconstantize # => "Backoffice" "Admin::Hotel::ReservationUtils".deconstantize # => "Admin::Hotel"
Active Support for example uses this method in Module#qualified_const_set
:
def qualified_const_set(path, value) QualifiedConstUtils.raise_if_absolute(path) const_name = path.demodulize mod_name = path.deconstantize mod = mod_name.empty? ? self : qualified_const_get(mod_name) mod.const_set(const_name, value) end
NOTE: Defined in active_support/core_ext/string/inflections.rb
.
parameterize
The method parameterize
normalizes its receiver in a way that can be used in pretty URLs.
"John Smith".parameterize # => "john-smith" "Kurt Gödel".parameterize # => "kurt-godel"
In fact, the result string is wrapped in an instance of ActiveSupport::Multibyte::Chars
.
NOTE: Defined in active_support/core_ext/string/inflections.rb
.
tableize
The method tableize
is underscore
followed by pluralize
.
"Person".tableize # => "people" "Invoice".tableize # => "invoices" "InvoiceLine".tableize # => "invoice_lines"
As a rule of thumb, tableize
returns the table name that corresponds to a given model for simple cases. The actual implementation in Active Record is not straight tableize
indeed, because it also demodulizes the class name and checks a few options that may affect the returned string.
NOTE: Defined in active_support/core_ext/string/inflections.rb
.
classify
The method classify
is the inverse of tableize
. It gives you the class name corresponding to a table name:
"people".classify # => "Person" "invoices".classify # => "Invoice" "invoice_lines".classify # => "InvoiceLine"
The method understands qualified table names:
"highrise_production.companies".classify # => "Company"
Note that classify
returns a class name as a string. You can get the actual class object invoking constantize
on it, explained next.
NOTE: Defined in active_support/core_ext/string/inflections.rb
.
constantize
The method constantize
resolves the constant reference expression in its receiver:
"Fixnum".constantize # => Fixnum module M X = 1 end "M::X".constantize # => 1
If the string evaluates to no known constant, or its content is not even a valid constant name, constantize
raises NameError
.
Constant name resolution by constantize
starts always at the top-level Object
even if there is no leading “::”.
X = :in_Object module M X = :in_M X # => :in_M "::X".constantize # => :in_Object "X".constantize # => :in_Object (!) end
So, it is in general not equivalent to what Ruby would do in the same spot, had a real constant be evaluated.
Mailer test cases obtain the mailer being tested from the name of the test class using constantize
:
# action_mailer/test_case.rb def determine_default_mailer(name) name.sub(/Test$/, '').constantize rescue NameError => e raise NonInferrableMailerError.new(name) end
NOTE: Defined in active_support/core_ext/string/inflections.rb
.
humanize
The method humanize
gives you a sensible name for display out of an attribute name. To do so it replaces underscores with spaces, removes any “_id” suffix, and capitalizes the first word:
"name".humanize # => "Name" "author_id".humanize # => "Author" "comments_count".humanize # => "Comments count"
The helper method full_messages
uses humanize
as a fallback to include attribute names:
def full_messages full_messages = [] each do |attribute, messages| ... attr_name = attribute.to_s.gsub('.', '_').humanize attr_name = @base.class.human_attribute_name(attribute, default: attr_name) ... end full_messages end
NOTE: Defined in active_support/core_ext/string/inflections.rb
.
foreign_key
The method foreign_key
gives a foreign key column name from a class name. To do so it demodulizes, underscores, and adds “_id”:
"User".foreign_key # => "user_id" "InvoiceLine".foreign_key # => "invoice_line_id" "Admin::Session".foreign_key # => "session_id"
Pass a false argument if you do not want the underscore in “_id”:
"User".foreign_key(false) # => "userid"
Associations use this method to infer foreign keys, for example has_one
and has_many
do this:
# active_record/associations.rb foreign_key = options[:foreign_key] || reflection.active_record.name.foreign_key
NOTE: Defined in active_support/core_ext/string/inflections.rb
.
to_date
, to_time
, to_datetime
The methods to_date
, to_time
, and to_datetime
are basically convenience wrappers around Date._parse
:
"2010-07-27".to_date # => Tue, 27 Jul 2010 "2010-07-27 23:37:00".to_time # => Tue Jul 27 23:37:00 UTC 2010 "2010-07-27 23:37:00".to_datetime # => Tue, 27 Jul 2010 23:37:00 +0000
to_time
receives an optional argument :utc
or :local
, to indicate which time zone you want the time in:
"2010-07-27 23:42:00".to_time(:utc) # => Tue Jul 27 23:42:00 UTC 2010 "2010-07-27 23:42:00".to_time(:local) # => Tue Jul 27 23:42:00 +0200 2010
Default is :utc
.
Please refer to the documentation of Date._parse
for further details.
INFO: The three of them return nil
for blank receivers.
NOTE: Defined in active_support/core_ext/string/conversions.rb
.
Numeric
All numbers respond to these methods:
bytes kilobytes megabytes gigabytes terabytes petabytes exabytes
They return the corresponding amount of bytes, using a conversion factor of 1024:
2.kilobytes # => 2048 3.megabytes # => 3145728 3.5.gigabytes # =><PHONE_NUMBER> -4.exabytes # => -4611686018427387904
Singular forms are aliased so you are able to say:
1.megabyte # => 1048576
NOTE: Defined in active_support/core_ext/numeric/bytes.rb
.
Enables the use of time calculations and declarations, like 45.minutes + 2.hours + 4.years
.
These methods use Time#advance for precise date calculations when using from_now, ago, etc. as well as adding or subtracting their results from a Time object. For example:
# equivalent to Time.current.advance(months: 1) 1.month.from_now # equivalent to Time.current.advance(years: 2) 2.years.from_now # equivalent to Time.current.advance(months: 4, years: 5) (4.months + 5.years).from_now
While these methods provide precise calculation when used as in the examples above, care
should be taken to note that this is not true if the result of months',
years’, etc is
converted before use:
# equivalent to 30.days.to_i.from_now 1.month.to_i.from_now # equivalent to 365.25.days.to_f.from_now 1.year.to_f.from_now
In such cases, Ruby’s core Date and Time should be used for precision date and time arithmetic.
NOTE: Defined in active_support/core_ext/numeric/time.rb
.
Enables the formatting of numbers in a variety of ways.
Produce a string representation of a number as a telephone number:
5551234.to_s(:phone) # => 555-1234<PHONE_NUMBER>.to_s(:phone) # =><PHONE_NUMBER><PHONE_NUMBER>.to_s(:phone, area_code: true) # =><PHONE_NUMBER><PHONE_NUMBER>.to_s(:phone, delimiter: " ") # =><PHONE_NUMBER><PHONE_NUMBER>.to_s(:phone, area_code: true, extension: 555) # =><PHONE_NUMBER> x<PHONE_NUMBER>234.to_s(:phone, country_code: 1) # => +1-123-555-1234
Produce a string representation of a number as currency:
1234567890.50.to_s(:currency) # => $1,234,567,890.50<PHONE_NUMBER>.506.to_s(:currency) # => $1,234,567,890.51<PHONE_NUMBER>.506.to_s(:currency, precision: 3) # => $1,234,567,890.506
Produce a string representation of a number as a percentage:
100.to_s(:percentage) # => 100.000% 100.to_s(:percentage, precision: 0) # => 100% 1000.to_s(:percentage, delimiter: '.', separator: ',') # => 1.000,000%<PHONE_NUMBER>3423.to_s(:percentage, precision: 5) # => 302.24399%
Produce a string representation of a number in delimited form:
12345678.to_s(:delimited) # => 12,345,678 12345678.05.to_s(:delimited) # => 12,345,678.05 12345678.to_s(:delimited, delimiter: ".") # => 12.345.678 12345678.to_s(:delimited, delimiter: ",") # => 12,345,678 12345678.05.to_s(:delimited, separator: " ") # => 12,345,678 05
Produce a string representation of a number rounded to a precision:
111.2345.to_s(:rounded) # => 111.235 111.2345.to_s(:rounded, precision: 2) # => 111.23 13.to_s(:rounded, precision: 5) # => 13.00000 389.32314.to_s(:rounded, precision: 0) # =><PHONE_NUMBER>.to_s(:rounded, significant: true) # => 111
Produce a string representation of a number as a human-readable number of bytes:
123.to_s(:human_size) # => 123 Bytes 1234.to_s(:human_size) # => 1.21 KB 12345.to_s(:human_size) # => 12.1 KB 1234567.to_s(:human_size) # => 1.18 MB<PHONE_NUMBER>.to_s(:human_size) # => 1.15 GB<PHONE_NUMBER>123.to_s(:human_size) # => 1.12 TB
Produce a string representation of a number in human-readable words:
123.to_s(:human) # => "123" 1234.to_s(:human) # => "1.23 Thousand" 12345.to_s(:human) # => "12.3 Thousand" 1234567.to_s(:human) # => "1.23 Million"<PHONE_NUMBER>.to_s(:human) # => "1.23 Billion"<PHONE_NUMBER>123.to_s(:human) # => "1.23 Trillion"<PHONE_NUMBER>123456.to_s(:human) # => "1.23 Quadrillion"
NOTE: Defined in active_support/core_ext/numeric/formatting.rb
.
Integer
multiple_of?
The method multiple_of?
tests whether an integer is multiple of the argument:
2.multiple_of?(1) # => true 1.multiple_of?(2) # => false
NOTE: Defined in active_support/core_ext/integer/multiple.rb
.
ordinal
The method ordinal
returns the ordinal suffix string corresponding to the receiver integer:
1.ordinal # => "st" 2.ordinal # => "nd" 53.ordinal # => "rd" 2009.ordinal # => "th" -21.ordinal # => "st" -134.ordinal # => "th"
NOTE: Defined in active_support/core_ext/integer/inflections.rb
.
ordinalize
The method ordinalize
returns the ordinal string corresponding to the receiver integer. In comparison, note that the ordinal
method returns only the suffix string.
1.ordinalize # => "1st" 2.ordinalize # => "2nd" 53.ordinalize # => "53rd" 2009.ordinalize # => "2009th" -21.ordinalize # => "-21st" -134.ordinalize # => "-134th"
NOTE: Defined in active_support/core_ext/integer/inflections.rb
.
BigDecimal
…
Enumerable
sum
The method sum
adds the elements of an enumerable:
[1, 2, 3].sum # => 6 (1..100).sum # => 5050
Addition only assumes the elements respond to +
:
[[1, 2], [2, 3], [3, 4]].sum # => [1, 2, 2, 3, 3, 4] %w(foo bar baz).sum # => "foobarbaz" {a: 1, b: 2, c: 3}.sum # => [:b, 2, :c, 3, :a, 1]
The sum of an empty collection is zero by default, but this is customizable:
[].sum # => 0 [].sum(1) # => 1
If a block is given, sum
becomes an iterator that yields the elements of the collection and sums the returned values:
(1..5).sum {|n| n * 2 } # => 30 [2, 4, 6, 8, 10].sum # => 30
The sum of an empty receiver can be customized in this form as well:
[].sum(1) {|n| n**3} # => 1
NOTE: Defined in active_support/core_ext/enumerable.rb
.
index_by
The method index_by
generates a hash with the elements of an enumerable indexed by some key.
It iterates through the collection and passes each element to a block. The element will be keyed by the value returned by the block:
invoices.index_by(&:number) # => {'2009-032' => <Invoice ...>, '2009-008' => <Invoice ...>, ...}
WARNING. Keys should normally be unique. If the block returns the same value for different elements no collection is built for that key. The last item will win.
NOTE: Defined in active_support/core_ext/enumerable.rb
.
many?
The method many?
is shorthand for collection.size > 1
:
<% if pages.many? %> <%= pagination_links %> <% end %>
If an optional block is given, many?
only takes into account those elements that return true:
@see_more = videos.many? {|video| video.category == params[:category]}
NOTE: Defined in active_support/core_ext/enumerable.rb
.
exclude?
The predicate exclude?
tests whether a given object does not belong to the collection. It is the negation of the built-in include?
:
to_visit << node if visited.exclude?(node)
NOTE: Defined in active_support/core_ext/enumerable.rb
.
Array
Active Support augments the API of arrays to ease certain ways of accessing them. For example, to
returns the subarray of elements up to the one at the passed index:
%w(a b c d).to(2) # => %w(a b c) [].to(7) # => []
Similarly, from
returns the tail from the element at the passed index to the end. If the index is greater than the length of the array, it returns an empty array.
%w(a b c d).from(2) # => %w(c d) %w(a b c d).from(10) # => [] [].from(0) # => []
The methods second
, third
, fourth
, and fifth
return the corresponding element (first
is built-in). Thanks to social wisdom and positive constructiveness all around, forty_two
is also available.
%w(a b c d).third # => c %w(a b c d).fifth # => nil
NOTE: Defined in active_support/core_ext/array/access.rb
.
prepend
This method is an alias of Array#unshift
.
%w(a b c d).prepend('e') # => %w(e a b c d) [].prepend(10) # => [10]
NOTE: Defined in active_support/core_ext/array/prepend_and_append.rb
.
append
This method is an alias of Array#<<
.
%w(a b c d).append('e') # => %w(a b c d e) [].append([1,2]) # => [[1,2]]
NOTE: Defined in active_support/core_ext/array/prepend_and_append.rb
.
When the last argument in a method call is a hash, except perhaps for a &block
argument, Ruby allows you to omit the brackets:
User.exists?(email: params[:email])
That syntactic sugar is used a lot in Rails to avoid positional arguments where there would be too many, offering instead interfaces that emulate named parameters. In particular it is very idiomatic to use a trailing hash for options.
If a method expects a variable number of arguments and uses *
in its declaration, however, such an options hash ends up being an item of the array of arguments, where it loses its role.
In those cases, you may give an options hash a distinguished treatment with extract_options!
. This method checks the type of the last item of an array. If it is a hash it pops it and returns it, otherwise it returns an empty hash.
Let’s see for example the definition of the caches_action
controller macro:
def caches_action(*actions) return unless cache_configured? options = actions.extract_options! ... end
This method receives an arbitrary number of action names, and an optional hash of options as last argument. With the call to extract_options!
you obtain the options hash and remove it from actions
in a simple and explicit way.
NOTE: Defined in active_support/core_ext/array/extract_options.rb
.
to_sentence
The method to_sentence
turns an array into a string containing a sentence that enumerates its items:
%w().to_sentence # => "" %w(Earth).to_sentence # => "Earth" %w(Earth Wind).to_sentence # => "Earth and Wind" %w(Earth Wind Fire).to_sentence # => "Earth, Wind, and Fire"
This method accepts three options:
:two_words_connector
: What is used for arrays of length 2. Default is “ and “.:words_connector
: What is used to join the elements of arrays with 3 or more elements, except for the last two. Default is “, “.:last_word_connector
: What is used to join the last items of an array with 3 or more elements. Default is “, and “.The defaults for these options can be localized, their keys are:
| Option | I18n key |
|---|---|
:two_words_connector |
support.array.two_words_connector |
:words_connector |
support.array.words_connector |
:last_word_connector |
support.array.last_word_connector |
Options :connector
and :skip_last_comma
are deprecated.
NOTE: Defined in active_support/core_ext/array/conversions.rb
.
to_formatted_s
The method to_formatted_s
acts like to_s
by default.
If the array contains items that respond to id
, however, the symbol
:db
may be passed as argument. That’s typically used with
collections of Active Record objects. Returned strings are:
[].to_formatted_s(:db) # => "null" [user].to_formatted_s(:db) # => "8456" invoice.lines.to_formatted_s(:db) # => "23,567,556,12"
Integers in the example above are supposed to come from the respective calls to id
.
NOTE: Defined in active_support/core_ext/array/conversions.rb
.
to_xml
The method to_xml
returns a string containing an XML representation of its receiver:
Contributor.limit(2).order(:rank).to_xml # => # <?xml version="1.0" encoding="UTF-8"?> # <contributors type="array"> # <contributor> # <id type="integer">4356</id> # <name>Jeremy Kemper</name> # <rank type="integer">1</rank> # <url-id>jeremy-kemper</url-id> # </contributor> # <contributor> # <id type="integer">4404</id> # <name>David Heinemeier Hansson</name> # <rank type="integer">2</rank> # <url-id>david-heinemeier-hansson</url-id> # </contributor> # </contributors>
To do so it sends to_xml
to every item in turn, and collects the results under a root node. All items must respond to to_xml
, an exception is raised otherwise.
By default, the name of the root element is the underscorized and dasherized plural of the name of the class of the first item, provided the rest of elements belong to that type (checked with is_a?
) and they are not hashes. In the example above that’s “contributors”.
If there’s any element that does not belong to the type of the first one the root node becomes “objects”:
[Contributor.first, Commit.first].to_xml # => # <?xml version="1.0" encoding="UTF-8"?> # <objects type="array"> # <object> # <id type="integer">4583</id> # <name>Aaron Batalion</name> # <rank type="integer">53</rank> # <url-id>aaron-batalion</url-id> # </object> # <object> # <author>Joshua Peek</author> # <authored-timestamp type="datetime">2009-09-02T16:44:36Z</authored-timestamp> # <branch>origin/master</branch> # <committed-timestamp type="datetime">2009-09-02T16:44:36Z</committed-timestamp> # <committer>Joshua Peek</committer> # <git-show nil="true"></git-show> # <id type="integer">190316</id> # <imported-from-svn type="boolean">false</imported-from-svn> # <message>Kill AMo observing wrap_with_notifications since ARes was only using it</message> # <sha1>723a47bfb3708f968821bc969a9a3fc873a3ed58</sha1> # </object> # </objects>
If the receiver is an array of hashes the root element is by default also “objects”:
[{a: 1, b: 2}, {c: 3}].to_xml # => # <?xml version="1.0" encoding="UTF-8"?> # <objects type="array"> # <object> # <b type="integer">2</b> # <a type="integer">1</a> # </object> # <object> # <c type="integer">3</c> # </object> # </objects>
WARNING. If the collection is empty the root element is by default “nil-classes”. That’s a gotcha, for example the root element of the list of contributors above would not be “contributors” if the collection was empty, but “nil-classes”. You may use the :root
option to ensure a consistent root element.
The name of children nodes is by default the name of the root node singularized. In the examples above we’ve seen “contributor” and “object”. The option :children
allows you to set these node names.
The default XML builder is a fresh instance of Builder::XmlMarkup
. You can configure your own builder via the :builder
option. The method also accepts options like :dasherize
and friends, they are forwarded to the builder:
Contributor.limit(2).order(:rank).to_xml(skip_types: true) # => # <?xml version="1.0" encoding="UTF-8"?> # <contributors> # <contributor> # <id>4356</id> # <name>Jeremy Kemper</name> # <rank>1</rank> # <url-id>jeremy-kemper</url-id> # </contributor> # <contributor> # <id>4404</id> # <name>David Heinemeier Hansson</name> # <rank>2</rank> # <url-id>david-heinemeier-hansson</url-id> # </contributor> # </contributors>
NOTE: Defined in active_support/core_ext/array/conversions.rb
.
The method Array.wrap
wraps its argument in an array unless it is already an array (or array-like).
Specifically:
nil
an empty list is returned.to_ary
it is invoked, and if the value of to_ary
is not nil
, it is returned.Array.wrap(nil) # => [] Array.wrap([1, 2, 3]) # => [1, 2, 3] Array.wrap(0) # => [0]
This method is similar in purpose to Kernel#Array
, but there are some differences:
to_ary
the method is invoked. Kernel#Array
moves on to try to_a
if the returned value is nil
, but Array.wrap
returns nil
right away.to_ary
is neither nil
nor an Array
object, Kernel#Array
raises an exception, while Array.wrap
does not, it just returns the value.to_a
on the argument, though special-cases nil
to return an empty array.The last point is particularly worth comparing for some enumerables:
Array.wrap(foo: :bar) # => [{:foo=>:bar}] Array(foo: :bar) # => [[:foo, :bar]]
There’s also a related idiom that uses the splat operator:
[*object]
which in Ruby 1.8 returns [nil]
for nil
, and calls to Array(object)
otherwise. (Please if you know the exact behavior in 1.9 contact fxn.)
Thus, in this case the behavior is different for nil
, and the differences with Kernel#Array
explained above apply to the rest of object
s.
NOTE: Defined in active_support/core_ext/array/wrap.rb
.
The method Array.deep_dup
duplicates itself and all objects inside
recursively with Active Support method Object#deep_dup
. It works like Array#map
with sending deep_dup
method to each object inside.
array = [1, [2, 3]] dup = array.deep_dup dup[1][2] = 4 array[1][2] == nil # => true
NOTE: Defined in active_support/core_ext/array/deep_dup.rb
.
in_groups_of(number, fill_with = nil)
The method in_groups_of
splits an array into consecutive groups of a certain size. It returns an array with the groups:
[1, 2, 3].in_groups_of(2) # => [[1, 2], [3, nil]]
or yields them in turn if a block is passed:
~~~html+erb <% sample.in_groups_of(3) do |a, b, c| %>
<% end %> ~~~
The first example shows in_groups_of
fills the last group with as many nil
elements as needed to have the requested size. You can change this padding value using the second optional argument:
[1, 2, 3].in_groups_of(2, 0) # => [[1, 2], [3, 0]]
And you can tell the method not to fill the last group passing false
:
[1, 2, 3].in_groups_of(2, false) # => [[1, 2], [3]]
As a consequence false
can’t be a used as a padding value.
NOTE: Defined in active_support/core_ext/array/grouping.rb
.
in_groups(number, fill_with = nil)
The method in_groups
splits an array into a certain number of groups. The method returns an array with the groups:
%w(1 2 3 4 5 6 7).in_groups(3) # => [["1", "2", "3"], ["4", "5", nil], ["6", "7", nil]]
or yields them in turn if a block is passed:
%w(1 2 3 4 5 6 7).in_groups(3) {|group| p group} ["1", "2", "3"] ["4", "5", nil] ["6", "7", nil]
The examples above show that in_groups
fills some groups with a trailing nil
element as needed. A group can get at most one of these extra elements, the rightmost one if any. And the groups that have them are always the last ones.
You can change this padding value using the second optional argument:
%w(1 2 3 4 5 6 7).in_groups(3, "0") # => [["1", "2", "3"], ["4", "5", "0"], ["6", "7", "0"]]
And you can tell the method not to fill the smaller groups passing false
:
%w(1 2 3 4 5 6 7).in_groups(3, false) # => [["1", "2", "3"], ["4", "5"], ["6", "7"]]
As a consequence false
can’t be a used as a padding value.
NOTE: Defined in active_support/core_ext/array/grouping.rb
.
split(value = nil)
The method split
divides an array by a separator and returns the resulting chunks.
If a block is passed the separators are those elements of the array for which the block returns true:
(-5..5).to_a.split { |i| i.multiple_of?(4) } # => [[-5], [-3, -2, -1], [1, 2, 3], [5]]
Otherwise, the value received as argument, which defaults to nil
, is the separator:
[0, 1, -5, 1, 1, "foo", "bar"].split(1) # => [[0], [-5], [], ["foo", "bar"]]
TIP: Observe in the previous example that consecutive separators result in empty arrays.
NOTE: Defined in active_support/core_ext/array/grouping.rb
.
Hash
to_xml
The method to_xml
returns a string containing an XML representation of its receiver:
{"foo" => 1, "bar" => 2}.to_xml # => # <?xml version="1.0" encoding="UTF-8"?> # <hash> # <foo type="integer">1</foo> # <bar type="integer">2</bar> # </hash>
To do so, the method loops over the pairs and builds nodes that depend on the values. Given a pair key
, value
:
If value
is a hash there’s a recursive call with key
as :root
.
If value
is an array there’s a recursive call with key
as :root
, and key
singularized as :children
.
If value
is a callable object it must expect one or two arguments. Depending on the arity, the callable is invoked with the options
hash as first argument with key
as :root
, and key
singularized as second argument. Its return value becomes a new node.
If value
responds to to_xml
the method is invoked with key
as :root
.
Otherwise, a node with key
as tag is created with a string representation of value
as text node. If value
is nil
an attribute “nil” set to “true” is added. Unless the option :skip_types
exists and is true, an attribute “type” is added as well according to the following mapping:
XML_TYPE_NAMES = { "Symbol" => "symbol", "Fixnum" => "integer", "Bignum" => "integer", "BigDecimal" => "decimal", "Float" => "float", "TrueClass" => "boolean", "FalseClass" => "boolean", "Date" => "date", "DateTime" => "datetime", "Time" => "datetime" }
By default the root node is “hash”, but that’s configurable via the :root
option.
The default XML builder is a fresh instance of Builder::XmlMarkup
. You can configure your own builder with the :builder
option. The method also accepts options like :dasherize
and friends, they are forwarded to the builder.
NOTE: Defined in active_support/core_ext/hash/conversions.rb
.
Ruby has a built-in method Hash#merge
that merges two hashes:
{a: 1, b: 1}.merge(a: 0, c: 2) # => {:a=>0, :b=>1, :c=>2}
Active Support defines a few more ways of merging hashes that may be convenient.
reverse_merge
and reverse_merge!
In case of collision the key in the hash of the argument wins in merge
. You can support option hashes with default values in a compact way with this idiom:
options = {length: 30, omission: "..."}.merge(options)
Active Support defines reverse_merge
in case you prefer this alternative notation:
options = options.reverse_merge(length: 30, omission: "...")
And a bang version reverse_merge!
that performs the merge in place:
options.reverse_merge!(length: 30, omission: "...")
WARNING. Take into account that reverse_merge!
may change the hash in the caller, which may or may not be a good idea.
NOTE: Defined in active_support/core_ext/hash/reverse_merge.rb
.
reverse_update
The method reverse_update
is an alias for reverse_merge!
, explained above.
WARNING. Note that reverse_update
has no bang.
NOTE: Defined in active_support/core_ext/hash/reverse_merge.rb
.
deep_merge
and deep_merge!
As you can see in the previous example if a key is found in both hashes the value in the one in the argument wins.
Active Support defines Hash#deep_merge
. In a deep merge, if a key is found in both hashes and their values are hashes in turn, then their merge becomes the value in the resulting hash:
{a: {b: 1}}.deep_merge(a: {c: 2}) # => {:a=>{:b=>1, :c=>2}}
The method deep_merge!
performs a deep merge in place.
NOTE: Defined in active_support/core_ext/hash/deep_merge.rb
.
The method Hash.deep_dup
duplicates itself and all keys and values
inside recursively with Active Support method Object#deep_dup
. It works like Enumerator#each_with_object
with sending deep_dup
method to each pair inside.
hash = { a: 1, b: { c: 2, d: [3, 4] } } dup = hash.deep_dup dup[:b][:e] = 5 dup[:b][:d] << 5 hash[:b][:e] == nil # => true hash[:b][:d] == [3, 4] # => true
NOTE: Defined in active_support/core_ext/hash/deep_dup.rb
.
The method diff
returns a hash that represents a diff of the receiver and the argument with the following logic:
Pairs key
, value
that exist in both hashes do not belong to the diff hash.
If both hashes have key
, but with different values, the pair in the receiver wins.
The rest is just merged.
{a: 1}.diff(a: 1) # => {}, first rule {a: 1}.diff(a: 2) # => {:a=>1}, second rule {a: 1}.diff(b: 2) # => {:a=>1, :b=>2}, third rule {a: 1, b: 2, c: 3}.diff(b: 1, c: 3, d: 4) # => {:a=>1, :b=>2, :d=>4}, all rules {}.diff({}) # => {} {a: 1}.diff({}) # => {:a=>1} {}.diff(a: 1) # => {:a=>1}
An important property of this diff hash is that you can retrieve the original hash by applying diff
twice:
hash.diff(hash2).diff(hash2) == hash
Diffing hashes may be useful for error messages related to expected option hashes for example.
NOTE: Defined in active_support/core_ext/hash/diff.rb
.
except
and except!
The method except
returns a hash with the keys in the argument list removed, if present:
{a: 1, b: 2}.except(:a) # => {:b=>2}
If the receiver responds to convert_key
, the method is called on each of the arguments. This allows except
to play nice with hashes with indifferent access for instance:
{a: 1}.with_indifferent_access.except(:a) # => {} {a: 1}.with_indifferent_access.except("a") # => {}
There’s also the bang variant except!
that removes keys in the very receiver.
NOTE: Defined in active_support/core_ext/hash/except.rb
.
transform_keys
and transform_keys!
The method transform_keys
accepts a block and returns a hash that has applied the block operations to each of the keys in the receiver:
{nil => nil, 1 => 1, a: :a}.transform_keys{ |key| key.to_s.upcase } # => {"" => nil, "A" => :a, "1" => 1}
The result in case of collision is undefined:
{"a" => 1, a: 2}.transform_keys{ |key| key.to_s.upcase } # => {"A" => 2}, in my test, can't rely on this result though
This method may be useful for example to build specialized conversions. For instance stringify_keys
and symbolize_keys
use transform_keys
to perform their key conversions:
def stringify_keys transform_keys{ |key| key.to_s } end ... def symbolize_keys transform_keys{ |key| key.to_sym rescue key } end
There’s also the bang variant transform_keys!
that applies the block operations to keys in the very receiver.
Besides that, one can use deep_transform_keys
and deep_transform_keys!
to perform the block operation on all the keys in the given hash and all the hashes nested into it. An example of the result is:
{nil => nil, 1 => 1, nested: {a: 3, 5 => 5}}.deep_transform_keys{ |key| key.to_s.upcase } # => {""=>nil, "1"=>1, "NESTED"=>{"A"=>3, "5"=>5}}
NOTE: Defined in active_support/core_ext/hash/keys.rb
.
stringify_keys
and stringify_keys!
The method stringify_keys
returns a hash that has a stringified version of the keys in the receiver. It does so by sending to_s
to them:
{nil => nil, 1 => 1, a: :a}.stringify_keys # => {"" => nil, "a" => :a, "1" => 1}
The result in case of collision is undefined:
{"a" => 1, a: 2}.stringify_keys # => {"a" => 2}, in my test, can't rely on this result though
This method may be useful for example to easily accept both symbols and strings as options. For instance ActionView::Helpers::FormHelper
defines:
def to_check_box_tag(options = {}, checked_value = "1", unchecked_value = "0") options = options.stringify_keys options["type"] = "checkbox" ... end
The second line can safely access the “type” key, and let the user to pass either :type
or “type”.
There’s also the bang variant stringify_keys!
that stringifies keys in the very receiver.
Besides that, one can use deep_stringify_keys
and deep_stringify_keys!
to stringify all the keys in the given hash and all the hashes nested into it. An example of the result is:
{nil => nil, 1 => 1, nested: {a: 3, 5 => 5}}.deep_stringify_keys # => {""=>nil, "1"=>1, "nested"=>{"a"=>3, "5"=>5}}
NOTE: Defined in active_support/core_ext/hash/keys.rb
.
symbolize_keys
and symbolize_keys!
The method symbolize_keys
returns a hash that has a symbolized version of the keys in the receiver, where possible. It does so by sending to_sym
to them:
{nil => nil, 1 => 1, "a" => "a"}.symbolize_keys # => {1=>1, nil=>nil, :a=>"a"}
WARNING. Note in the previous example only one key was symbolized.
The result in case of collision is undefined:
{"a" => 1, a: 2}.symbolize_keys # => {:a=>2}, in my test, can't rely on this result though
This method may be useful for example to easily accept both symbols and strings as options. For instance ActionController::UrlRewriter
defines
def rewrite_path(options) options = options.symbolize_keys options.update(options[:params].symbolize_keys) if options[:params] ... end
The second line can safely access the :params
key, and let the user to pass either :params
or “params”.
There’s also the bang variant symbolize_keys!
that symbolizes keys in the very receiver.
Besides that, one can use deep_symbolize_keys
and deep_symbolize_keys!
to symbolize all the keys in the given hash and all the hashes nested into it. An example of the result is:
{nil => nil, 1 => 1, "nested" => {"a" => 3, 5 => 5}}.deep_symbolize_keys # => {nil=>nil, 1=>1, nested:{a:3, 5=>5}}
NOTE: Defined in active_support/core_ext/hash/keys.rb
.
to_options
and to_options!
The methods to_options
and to_options!
are respectively aliases of symbolize_keys
and symbolize_keys!
.
NOTE: Defined in active_support/core_ext/hash/keys.rb
.
assert_valid_keys
The method assert_valid_keys
receives an arbitrary number of arguments, and checks whether the receiver has any key outside that white list. If it does ArgumentError
is raised.
{a: 1}.assert_valid_keys(:a) # passes {a: 1}.assert_valid_keys("a") # ArgumentError
Active Record does not accept unknown options when building associations, for example. It implements that control via assert_valid_keys
.
NOTE: Defined in active_support/core_ext/hash/keys.rb
.
Ruby has built-in support for taking slices out of strings and arrays. Active Support extends slicing to hashes:
{a: 1, b: 2, c: 3}.slice(:a, :c) # => {:c=>3, :a=>1} {a: 1, b: 2, c: 3}.slice(:b, :X) # => {:b=>2} # non-existing keys are ignored
If the receiver responds to convert_key
keys are normalized:
{a: 1, b: 2}.with_indifferent_access.slice("a") # => {:a=>1}
NOTE. Slicing may come in handy for sanitizing option hashes with a white list of keys.
There’s also slice!
which in addition to perform a slice in place returns what’s removed:
hash = {a: 1, b: 2} rest = hash.slice!(:a) # => {:b=>2} hash # => {:a=>1}
NOTE: Defined in active_support/core_ext/hash/slice.rb
.
The method extract!
removes and returns the key/value pairs matching the given keys.
hash = {a: 1, b: 2} rest = hash.extract!(:a) # => {:a=>1} hash # => {:b=>2}
The method extract!
returns the same subclass of Hash, that the receiver is.
hash = {a: 1, b: 2}.with_indifferent_access rest = hash.extract!(:a).class # => ActiveSupport::HashWithIndifferentAccess
NOTE: Defined in active_support/core_ext/hash/slice.rb
.
The method with_indifferent_access
returns an ActiveSupport::HashWithIndifferentAccess
out of its receiver:
{a: 1}.with_indifferent_access["a"] # => 1
NOTE: Defined in active_support/core_ext/hash/indifferent_access.rb
.
Regexp
multiline?
The method multiline?
says whether a regexp has the /m
flag set, that is, whether the dot matches newlines.
%r{.}.multiline? # => false %r{.}m.multiline? # => true Regexp.new('.').multiline? # => false Regexp.new('.', Regexp::MULTILINE).multiline? # => true
Rails uses this method in a single place, also in the routing code. Multiline regexps are disallowed for route requirements and this flag eases enforcing that constraint.
def assign_route_options(segments, defaults, requirements) ... if requirement.multiline? raise ArgumentError, "Regexp multiline option not allowed in routing requirements: #{requirement.inspect}" end ... end
NOTE: Defined in active_support/core_ext/regexp.rb
.
Range
to_s
Active Support extends the method Range#to_s
so that it understands an optional format argument. As of this writing the only supported non-default format is :db
:
(Date.today..Date.tomorrow).to_s # => "2009-10-25..2009-10-26" (Date.today..Date.tomorrow).to_s(:db) # => "BETWEEN '2009-10-25' AND '2009-10-26'"
As the example depicts, the :db
format generates a BETWEEN
SQL clause. That is used by Active Record in its support for range values in conditions.
NOTE: Defined in active_support/core_ext/range/conversions.rb
.
include?
The methods Range#include?
and Range#===
say whether some value falls between the ends of a given instance:
(2..3).include?(Math::E) # => true
Active Support extends these methods so that the argument may be another range in turn. In that case we test whether the ends of the argument range belong to the receiver themselves:
(1..10).include?(3..7) # => true (1..10).include?(0..7) # => false (1..10).include?(3..11) # => false (1...9).include?(3..9) # => false (1..10) === (3..7) # => true (1..10) === (0..7) # => false (1..10) === (3..11) # => false (1...9) === (3..9) # => false
NOTE: Defined in active_support/core_ext/range/include_range.rb
.
overlaps?
The method Range#overlaps?
says whether any two given ranges have non-void intersection:
(1..10).overlaps?(7..11) # => true (1..10).overlaps?(0..7) # => true (1..10).overlaps?(11..27) # => false
NOTE: Defined in active_support/core_ext/range/overlaps.rb
.
Proc
bind
As you surely know Ruby has an UnboundMethod
class whose instances are methods that belong to the limbo of methods without a self. The method Module#instance_method
returns an unbound method for example:
Hash.instance_method(:delete) # => #<UnboundMethod: Hash#delete>
An unbound method is not callable as is, you need to bind it first to an object with bind
:
clear = Hash.instance_method(:clear) clear.bind({a: 1}).call # => {}
Active Support defines Proc#bind
with an analogous purpose:
Proc.new { size }.bind([]).call # => 0
As you see that’s callable and bound to the argument, the return value is indeed a Method
.
NOTE: To do so Proc#bind
actually creates a method under the hood. If you ever see a method with a weird name like __bind_1256598120_237302
in a stack trace you know now where it comes from.
Action Pack uses this trick in rescue_from
for example, which accepts the name of a method and also a proc as callbacks for a given rescued exception. It has to call them in either case, so a bound method is returned by handler_for_rescue
, thus simplifying the code in the caller:
def handler_for_rescue(exception) _, rescuer = Array(rescue_handlers).reverse.detect do |klass_name, handler| ... end case rescuer when Symbol method(rescuer) when Proc rescuer.bind(self) end end
NOTE: Defined in active_support/core_ext/proc.rb
.
Date
NOTE: All the following methods are defined in active_support/core_ext/date/calculations.rb
.
INFO: The following calculation methods have edge cases in October 1582, since days 5..14 just do not exist. This guide does not document their behavior around those days for brevity, but it is enough to say that they do what you would expect. That is, Date.new(1582, 10, 4).tomorrow
returns Date.new(1582, 10, 15)
and so on. Please check test/core_ext/date_ext_test.rb
in the Active Support test suite for expected behavior.
Date.current
Active Support defines Date.current
to be today in the current time zone. That’s like Date.today
, except that it honors the user time zone, if defined. It also defines Date.yesterday
and Date.tomorrow
, and the instance predicates past?
, today?
, and future?
, all of them relative to Date.current
.
When making Date comparisons using methods which honor the user time zone, make sure to use Date.current
and not Date.today
. There are cases where the user time zone might be in the future compared to the system time zone, which Date.today
uses by default. This means Date.today
may equal Date.yesterday
.
prev_year
, next_year
In Ruby 1.9 prev_year
and next_year
return a date with the same day/month in the last or next year:
d = Date.new(2010, 5, 8) # => Sat, 08 May 2010 d.prev_year # => Fri, 08 May 2009 d.next_year # => Sun, 08 May 2011
If date is the 29th of February of a leap year, you obtain the 28th:
d = Date.new(2000, 2, 29) # => Tue, 29 Feb 2000 d.prev_year # => Sun, 28 Feb 1999 d.next_year # => Wed, 28 Feb 2001
prev_year
is aliased to last_year
.
prev_month
, next_month
In Ruby 1.9 prev_month
and next_month
return the date with the same day in the last or next month:
d = Date.new(2010, 5, 8) # => Sat, 08 May 2010 d.prev_month # => Thu, 08 Apr 2010 d.next_month # => Tue, 08 Jun 2010
If such a day does not exist, the last day of the corresponding month is returned:
Date.new(2000, 5, 31).prev_month # => Sun, 30 Apr 2000 Date.new(2000, 3, 31).prev_month # => Tue, 29 Feb 2000 Date.new(2000, 5, 31).next_month # => Fri, 30 Jun 2000 Date.new(2000, 1, 31).next_month # => Tue, 29 Feb 2000
prev_month
is aliased to last_month
.
prev_quarter
, next_quarter
Same as prev_month
and next_month
. It returns the date with the same day in the previous or next quarter:
t = Time.local(2010, 5, 8) # => Sat, 08 May 2010 t.prev_quarter # => Mon, 08 Feb 2010 t.next_quarter # => Sun, 08 Aug 2010
If such a day does not exist, the last day of the corresponding month is returned:
Time.local(2000, 7, 31).prev_quarter # => Sun, 30 Apr 2000 Time.local(2000, 5, 31).prev_quarter # => Tue, 29 Feb 2000 Time.local(2000, 10, 31).prev_quarter # => Mon, 30 Oct 2000 Time.local(2000, 11, 31).next_quarter # => Wed, 28 Feb 2001
prev_quarter
is aliased to last_quarter
.
beginning_of_week
, end_of_week
The methods beginning_of_week
and end_of_week
return the dates for the
beginning and end of the week, respectively. Weeks are assumed to start on
Monday, but that can be changed passing an argument, setting thread local
Date.beginning_of_week
or config.beginning_of_week
.
d = Date.new(2010, 5, 8) # => Sat, 08 May 2010 d.beginning_of_week # => Mon, 03 May 2010 d.beginning_of_week(:sunday) # => Sun, 02 May 2010 d.end_of_week # => Sun, 09 May 2010 d.end_of_week(:sunday) # => Sat, 08 May 2010
beginning_of_week
is aliased to at_beginning_of_week
and end_of_week
is aliased to at_end_of_week
.
monday
, sunday
The methods monday
and sunday
return the dates for the previous Monday and
next Sunday, respectively.
d = Date.new(2010, 5, 8) # => Sat, 08 May 2010 d.monday # => Mon, 03 May 2010 d.sunday # => Sun, 09 May 2010 d = Date.new(2012, 9, 10) # => Mon, 10 Sep 2012 d.monday # => Mon, 10 Sep 2012 d = Date.new(2012, 9, 16) # => Sun, 16 Sep 2012 d.sunday # => Sun, 16 Sep 2012
prev_week
, next_week
The method next_week
receives a symbol with a day name in English (default is the thread local Date.beginning_of_week
, or config.beginning_of_week
, or :monday
) and it returns the date corresponding to that day.
d = Date.new(2010, 5, 9) # => Sun, 09 May 2010 d.next_week # => Mon, 10 May 2010 d.next_week(:saturday) # => Sat, 15 May 2010
The method prev_week
is analogous:
d.prev_week # => Mon, 26 Apr 2010 d.prev_week(:saturday) # => Sat, 01 May 2010 d.prev_week(:friday) # => Fri, 30 Apr 2010
prev_week
is aliased to last_week
.
Both next_week
and prev_week
work as expected when Date.beginning_of_week
or config.beginning_of_week
are set.
beginning_of_month
, end_of_month
The methods beginning_of_month
and end_of_month
return the dates for the beginning and end of the month:
d = Date.new(2010, 5, 9) # => Sun, 09 May 2010 d.beginning_of_month # => Sat, 01 May 2010 d.end_of_month # => Mon, 31 May 2010
beginning_of_month
is aliased to at_beginning_of_month
, and end_of_month
is aliased to at_end_of_month
.
beginning_of_quarter
, end_of_quarter
The methods beginning_of_quarter
and end_of_quarter
return the dates for the beginning and end of the quarter of the receiver’s calendar year:
d = Date.new(2010, 5, 9) # => Sun, 09 May 2010 d.beginning_of_quarter # => Thu, 01 Apr 2010 d.end_of_quarter # => Wed, 30 Jun 2010
beginning_of_quarter
is aliased to at_beginning_of_quarter
, and end_of_quarter
is aliased to at_end_of_quarter
.
beginning_of_year
, end_of_year
The methods beginning_of_year
and end_of_year
return the dates for the beginning and end of the year:
d = Date.new(2010, 5, 9) # => Sun, 09 May 2010 d.beginning_of_year # => Fri, 01 Jan 2010 d.end_of_year # => Fri, 31 Dec 2010
beginning_of_year
is aliased to at_beginning_of_year
, and end_of_year
is aliased to at_end_of_year
.
years_ago
, years_since
The method years_ago
receives a number of years and returns the same date those many years ago:
date = Date.new(2010, 6, 7) date.years_ago(10) # => Wed, 07 Jun 2000
years_since
moves forward in time:
date = Date.new(2010, 6, 7) date.years_since(10) # => Sun, 07 Jun 2020
If such a day does not exist, the last day of the corresponding month is returned:
Date.new(2012, 2, 29).years_ago(3) # => Sat, 28 Feb 2009 Date.new(2012, 2, 29).years_since(3) # => Sat, 28 Feb 2015
months_ago
, months_since
The methods months_ago
and months_since
work analogously for months:
Date.new(2010, 4, 30).months_ago(2) # => Sun, 28 Feb 2010 Date.new(2010, 4, 30).months_since(2) # => Wed, 30 Jun 2010
If such a day does not exist, the last day of the corresponding month is returned:
Date.new(2010, 4, 30).months_ago(2) # => Sun, 28 Feb 2010 Date.new(2009, 12, 31).months_since(2) # => Sun, 28 Feb 2010
weeks_ago
The method weeks_ago
works analogously for weeks:
Date.new(2010, 5, 24).weeks_ago(1) # => Mon, 17 May 2010 Date.new(2010, 5, 24).weeks_ago(2) # => Mon, 10 May 2010
advance
The most generic way to jump to other days is advance
. This method receives a hash with keys :years
, :months
, :weeks
, :days
, and returns a date advanced as much as the present keys indicate:
date = Date.new(2010, 6, 6) date.advance(years: 1, weeks: 2) # => Mon, 20 Jun 2011 date.advance(months: 2, days: -2) # => Wed, 04 Aug 2010
Note in the previous example that increments may be negative.
To perform the computation the method first increments years, then months, then weeks, and finally days. This order is important towards the end of months. Say for example we are at the end of February of 2010, and we want to move one month and one day forward.
The method advance
advances first one month, and then one day, the result is:
Date.new(2010, 2, 28).advance(months: 1, days: 1) # => Sun, 29 Mar 2010
While if it did it the other way around the result would be different:
Date.new(2010, 2, 28).advance(days: 1).advance(months: 1) # => Thu, 01 Apr 2010
The method change
allows you to get a new date which is the same as the receiver except for the given year, month, or day:
Date.new(2010, 12, 23).change(year: 2011, month: 11) # => Wed, 23 Nov 2011
This method is not tolerant to non-existing dates, if the change is invalid ArgumentError
is raised:
Date.new(2010, 1, 31).change(month: 2) # => ArgumentError: invalid date
Durations can be added to and subtracted from dates:
d = Date.current # => Mon, 09 Aug 2010 d + 1.year # => Tue, 09 Aug 2011 d - 3.hours # => Sun, 08 Aug 2010 21:00:00 UTC +00:00
They translate to calls to since
or advance
. For example here we get the correct jump in the calendar reform:
Date.new(1582, 10, 4) + 1.day # => Fri, 15 Oct 1582
INFO: The following methods return a Time
object if possible, otherwise a DateTime
. If set, they honor the user time zone.
beginning_of_day
, end_of_day
The method beginning_of_day
returns a timestamp at the beginning of the day (00:00:00):
date = Date.new(2010, 6, 7) date.beginning_of_day # => Mon Jun 07 00:00:00 +0200 2010
The method end_of_day
returns a timestamp at the end of the day (23:59:59):
date = Date.new(2010, 6, 7) date.end_of_day # => Mon Jun 07 23:59:59 +0200 2010
beginning_of_day
is aliased to at_beginning_of_day
, midnight
, at_midnight
.
beginning_of_hour
, end_of_hour
The method beginning_of_hour
returns a timestamp at the beginning of the hour (hh:00:00):
date = DateTime.new(2010, 6, 7, 19, 55, 25) date.beginning_of_hour # => Mon Jun 07 19:00:00 +0200 2010
The method end_of_hour
returns a timestamp at the end of the hour (hh:59:59):
date = DateTime.new(2010, 6, 7, 19, 55, 25) date.end_of_hour # => Mon Jun 07 19:59:59 +0200 2010
beginning_of_hour
is aliased to at_beginning_of_hour
.
beginning_of_minute
, end_of_minute
The method beginning_of_minute
returns a timestamp at the beginning of the minute (hh:mm:00):
date = DateTime.new(2010, 6, 7, 19, 55, 25) date.beginning_of_minute # => Mon Jun 07 19:55:00 +0200 2010
The method end_of_minute
returns a timestamp at the end of the minute (hh:mm:59):
date = DateTime.new(2010, 6, 7, 19, 55, 25) date.end_of_minute # => Mon Jun 07 19:55:59 +0200 2010
beginning_of_minute
is aliased to at_beginning_of_minute
.
INFO: beginning_of_hour
, end_of_hour
, beginning_of_minute
and end_of_minute
are implemented for Time
and DateTime
but not Date
as it does not make sense to request the beginning or end of an hour or minute on a Date
instance.
ago
, since
The method ago
receives a number of seconds as argument and returns a timestamp those many seconds ago from midnight:
date = Date.current # => Fri, 11 Jun 2010 date.ago(1) # => Thu, 10 Jun 2010 23:59:59 EDT -04:00
Similarly, since
moves forward:
date = Date.current # => Fri, 11 Jun 2010 date.since(1) # => Fri, 11 Jun 2010 00:00:01 EDT -04:00
DateTime
WARNING: DateTime
is not aware of DST rules and so some of these methods have edge cases when a DST change is going on. For example seconds_since_midnight
might not return the real amount in such a day.
NOTE: All the following methods are defined in active_support/core_ext/date_time/calculations.rb
.
The class DateTime
is a subclass of Date
so by loading active_support/core_ext/date/calculations.rb
you inherit these methods and their aliases, except that they will always return datetimes:
yesterday tomorrow beginning_of_week (at_beginning_of_week) end_of_week (at_end_of_week) monday sunday weeks_ago prev_week (last_week) next_week months_ago months_since beginning_of_month (at_beginning_of_month) end_of_month (at_end_of_month) prev_month (last_month) next_month beginning_of_quarter (at_beginning_of_quarter) end_of_quarter (at_end_of_quarter) beginning_of_year (at_beginning_of_year) end_of_year (at_end_of_year) years_ago years_since prev_year (last_year) next_year
The following methods are reimplemented so you do not need to load active_support/core_ext/date/calculations.rb
for these ones:
beginning_of_day (midnight, at_midnight, at_beginning_of_day)
end_of_day
ago
since (in)
On the other hand, advance
and change
are also defined and support more options, they are documented below.
The following methods are only implemented in active_support/core_ext/date_time/calculations.rb
as they only make sense when used with a DateTime
instance:
beginning_of_hour (at_beginning_of_hour) end_of_hour
DateTime.current
Active Support defines DateTime.current
to be like Time.now.to_datetime
, except that it honors the user time zone, if defined. It also defines DateTime.yesterday
and DateTime.tomorrow
, and the instance predicates past?
, and future?
relative to DateTime.current
.
seconds_since_midnight
The method seconds_since_midnight
returns the number of seconds since midnight:
now = DateTime.current # => Mon, 07 Jun 2010 20:26:36 +0000 now.seconds_since_midnight # => 73596
utc
The method utc
gives you the same datetime in the receiver expressed in UTC.
now = DateTime.current # => Mon, 07 Jun 2010 19:27:52 -0400 now.utc # => Mon, 07 Jun 2010 23:27:52 +0000
This method is also aliased as getutc
.
utc?
The predicate utc?
says whether the receiver has UTC as its time zone:
now = DateTime.now # => Mon, 07 Jun 2010 19:30:47 -0400 now.utc? # => false now.utc.utc? # => true
advance
The most generic way to jump to another datetime is advance
. This method receives a hash with keys :years
, :months
, :weeks
, :days
, :hours
, :minutes
, and :seconds
, and returns a datetime advanced as much as the present keys indicate.
d = DateTime.current # => Thu, 05 Aug 2010 11:33:31 +0000 d.advance(years: 1, months: 1, days: 1, hours: 1, minutes: 1, seconds: 1) # => Tue, 06 Sep 2011 12:34:32 +0000
This method first computes the destination date passing :years
, :months
, :weeks
, and :days
to Date#advance
documented above. After that, it adjusts the time calling since
with the number of seconds to advance. This order is relevant, a different ordering would give different datetimes in some edge-cases. The example in Date#advance
applies, and we can extend it to show order relevance related to the time bits.
If we first move the date bits (that have also a relative order of processing, as documented before), and then the time bits we get for example the following computation:
d = DateTime.new(2010, 2, 28, 23, 59, 59) # => Sun, 28 Feb 2010 23:59:59 +0000 d.advance(months: 1, seconds: 1) # => Mon, 29 Mar 2010 00:00:00 +0000
but if we computed them the other way around, the result would be different:
d.advance(seconds: 1).advance(months: 1) # => Thu, 01 Apr 2010 00:00:00 +0000
WARNING: Since DateTime
is not DST-aware you can end up in a non-existing point in time with no warning or error telling you so.
The method change
allows you to get a new datetime which is the same as the receiver except for the given options, which may include :year
, :month
, :day
, :hour
, :min
, :sec
, :offset
, :start
:
now = DateTime.current # => Tue, 08 Jun 2010 01:56:22 +0000 now.change(year: 2011, offset: Rational(-6, 24)) # => Wed, 08 Jun 2011 01:56:22 -0600
If hours are zeroed, then minutes and seconds are too (unless they have given values):
now.change(hour: 0) # => Tue, 08 Jun 2010 00:00:00 +0000
Similarly, if minutes are zeroed, then seconds are too (unless it has given a value):
now.change(min: 0) # => Tue, 08 Jun 2010 01:00:00 +0000
This method is not tolerant to non-existing dates, if the change is invalid ArgumentError
is raised:
DateTime.current.change(month: 2, day: 30) # => ArgumentError: invalid date
Durations can be added to and subtracted from datetimes:
now = DateTime.current # => Mon, 09 Aug 2010 23:15:17 +0000 now + 1.year # => Tue, 09 Aug 2011 23:15:17 +0000 now - 1.week # => Mon, 02 Aug 2010 23:15:17 +0000
They translate to calls to since
or advance
. For example here we get the correct jump in the calendar reform:
DateTime.new(1582, 10, 4, 23) + 1.hour # => Fri, 15 Oct 1582 00:00:00 +0000
Time
NOTE: All the following methods are defined in active_support/core_ext/time/calculations.rb
.
Active Support adds to Time
many of the methods available for DateTime
:
past?
today?
future?
yesterday
tomorrow
seconds_since_midnight
change
advance
ago
since (in)
beginning_of_day (midnight, at_midnight, at_beginning_of_day)
end_of_day
beginning_of_hour (at_beginning_of_hour)
end_of_hour
beginning_of_week (at_beginning_of_week)
end_of_week (at_end_of_week)
monday
sunday
weeks_ago
prev_week (last_week)
next_week
months_ago
months_since
beginning_of_month (at_beginning_of_month)
end_of_month (at_end_of_month)
prev_month (last_month)
next_month
beginning_of_quarter (at_beginning_of_quarter)
end_of_quarter (at_end_of_quarter)
beginning_of_year (at_beginning_of_year)
end_of_year (at_end_of_year)
years_ago
years_since
prev_year (last_year)
next_year
They are analogous. Please refer to their documentation above and take into account the following differences:
change
accepts an additional :usec
option.Time
understands DST, so you get correct DST calculations as inTime.zone_default # => #<ActiveSupport::TimeZone:0x7f73654d4f38 @utc_offset=nil, @name="Madrid", ...> # In Barcelona, 2010/03/28 02:00 +0100 becomes 2010/03/28 03:00 +0200 due to DST. t = Time.local(2010, 3, 28, 1, 59, 59) # => Sun Mar 28 01:59:59 +0100 2010 t.advance(seconds: 1) # => Sun Mar 28 03:00:00 +0200 2010
since
or ago
jump to a time that can’t be expressed with Time
a DateTime
object is returned instead.Time.current
Active Support defines Time.current
to be today in the current time zone. That’s like Time.now
, except that it honors the user time zone, if defined. It also defines Time.yesterday
and Time.tomorrow
, and the instance predicates past?
, today?
, and future?
, all of them relative to Time.current
.
When making Time comparisons using methods which honor the user time zone, make sure to use Time.current
and not Time.now
. There are cases where the user time zone might be in the future compared to the system time zone, which Time.today
uses by default. This means Time.now
may equal Time.yesterday
.
all_day
, all_week
, all_month
, all_quarter
and all_year
The method all_day
returns a range representing the whole day of the current time.
now = Time.current # => Mon, 09 Aug 2010 23:20:05 UTC +00:00 now.all_day # => Mon, 09 Aug 2010 00:00:00 UTC +00:00..Mon, 09 Aug 2010 23:59:59 UTC +00:00
Analogously, all_week
, all_month
, all_quarter
and all_year
all serve the purpose of generating time ranges.
now = Time.current # => Mon, 09 Aug 2010 23:20:05 UTC +00:00 now.all_week # => Mon, 09 Aug 2010 00:00:00 UTC +00:00..Sun, 15 Aug 2010 23:59:59 UTC +00:00 now.all_week(:sunday) # => Sun, 16 Sep 2012 00:00:00 UTC +00:00..Sat, 22 Sep 2012 23:59:59 UTC +00:00 now.all_month # => Sat, 01 Aug 2010 00:00:00 UTC +00:00..Tue, 31 Aug 2010 23:59:59 UTC +00:00 now.all_quarter # => Thu, 01 Jul 2010 00:00:00 UTC +00:00..Thu, 30 Sep 2010 23:59:59 UTC +00:00 now.all_year # => Fri, 01 Jan 2010 00:00:00 UTC +00:00..Fri, 31 Dec 2010 23:59:59 UTC +00:00
Active Support defines Time.current
to be Time.zone.now
if there’s a user time zone defined, with fallback to Time.now
:
Time.zone_default # => #<ActiveSupport::TimeZone:0x7f73654d4f38 @utc_offset=nil, @name="Madrid", ...> Time.current # => Fri, 06 Aug 2010 17:11:58 CEST +02:00
Analogously to DateTime
, the predicates past?
, and future?
are relative to Time.current
.
If the time to be constructed lies beyond the range supported by Time
in the runtime platform, usecs are discarded and a DateTime
object is returned instead.
Durations can be added to and subtracted from time objects:
now = Time.current # => Mon, 09 Aug 2010 23:20:05 UTC +00:00 now + 1.year # => Tue, 09 Aug 2011 23:21:11 UTC +00:00 now - 1.week # => Mon, 02 Aug 2010 23:21:11 UTC +00:00
They translate to calls to since
or advance
. For example here we get the correct jump in the calendar reform:
Time.utc(1582, 10, 3) + 5.days # => Mon Oct 18 00:00:00 UTC 1582
File
atomic_write
With the class method File.atomic_write
you can write to a file in a way that will prevent any reader from seeing half-written content.
The name of the file is passed as an argument, and the method yields a file handle opened for writing. Once the block is done atomic_write
closes the file handle and completes its job.
For example, Action Pack uses this method to write asset cache files like all.css
:
File.atomic_write(joined_asset_path) do |cache| cache.write(join_asset_file_contents(asset_paths)) end
To accomplish this atomic_write
creates a temporary file. That’s the file the code in the block actually writes to. On completion, the temporary file is renamed, which is an atomic operation on POSIX systems. If the target file exists atomic_write
overwrites it and keeps owners and permissions. However there are a few cases where atomic_write
cannot change the file ownership or permissions, this error is caught and skipped over trusting in the user/filesystem to ensure the file is accessible to the processes that need it.
NOTE. Due to the chmod operation atomic_write
performs, if the target file has an ACL set on it this ACL will be recalculated/modified.
WARNING. Note you can’t append with atomic_write
.
The auxiliary file is written in a standard directory for temporary files, but you can pass a directory of your choice as second argument.
NOTE: Defined in active_support/core_ext/file/atomic.rb
.
Marshal
load
Active Support adds constant autoloading support to load
.
For example, the file cache store deserializes this way:
File.open(file_name) { |f| Marshal.load(f) }
If the cached data refers to a constant that is unknown at that point, the autoloading mechanism is triggered and if it succeeds the deserialization is retried transparently.
WARNING. If the argument is an IO
it needs to respond to rewind
to be able to retry. Regular files respond to rewind
.
NOTE: Defined in active_support/core_ext/marshal.rb
.
Logger
around_[level]
Takes two arguments, a before_message
and after_message
and calls the current level method on the Logger
instance, passing in the before_message
, then the specified message, then the after_message
:
logger = Logger.new("log/development.log") logger.around_info("before", "after") { |logger| logger.info("during") }
silence
Silences every log level lesser to the specified one for the duration of the given block. Log level orders are: debug, info, error and fatal.
logger = Logger.new("log/development.log") logger.silence(Logger::INFO) do logger.debug("In space, no one can hear you scream.") logger.info("Scream all you want, small mailman!") end
datetime_format=
Modifies the datetime format output by the formatter class associated with this logger. If the formatter class does not have a datetime_format
method then this is ignored.
class Logger::FormatWithTime < Logger::Formatter cattr_accessor(:datetime_format) { "%Y%m%d%H%m%S" } def self.call(severity, timestamp, progname, msg) "#{timestamp.strftime(datetime_format)} -- #{String === msg ? msg : msg.inspect}\n" end end logger = Logger.new("log/development.log") logger.formatter = Logger::FormatWithTime logger.info("<- is the current time")
NOTE: Defined in active_support/core_ext/logger.rb
.
NameError
Active Support adds missing_name?
to NameError
, which tests whether the exception was raised because of the name passed as argument.
The name may be given as a symbol or string. A symbol is tested against the bare constant name, a string is against the fully-qualified constant name.
TIP: A symbol can represent a fully-qualified constant name as in :"ActiveRecord::Base"
, so the behavior for symbols is defined for convenience, not because it has to be that way technically.
For example, when an action of PostsController
is called Rails tries optimistically to use PostsHelper
. It is OK that the helper module does not exist, so if an exception for that constant name is raised it should be silenced. But it could be the case that posts_helper.rb
raises a NameError
due to an actual unknown constant. That should be reraised. The method missing_name?
provides a way to distinguish both cases:
def default_helper_module! module_name = name.sub(/Controller$/, '') module_path = module_name.underscore helper module_path rescue MissingSourceFile => e raise e unless e.is_missing? "#{module_path}_helper" rescue NameError => e raise e unless e.missing_name? "#{module_name}Helper" end
NOTE: Defined in active_support/core_ext/name_error.rb
.
LoadError
Active Support adds is_missing?
to LoadError
, and also assigns that class to the constant MissingSourceFile
for backwards compatibility.
Given a path name is_missing?
tests whether the exception was raised due to that particular file (except perhaps for the “.rb” extension).
For example, when an action of PostsController
is called Rails tries to load posts_helper.rb
, but that file may not exist. That’s fine, the helper module is not mandatory so Rails silences a load error. But it could be the case that the helper module does exist and in turn requires another library that is missing. In that case Rails must reraise the exception. The method is_missing?
provides a way to distinguish both cases:
def default_helper_module! module_name = name.sub(/Controller$/, '') module_path = module_name.underscore helper module_path rescue MissingSourceFile => e raise e unless e.is_missing? "helpers/#{module_path}_helper" rescue NameError => e raise e unless e.missing_name? "#{module_name}Helper" end
NOTE: Defined in active_support/core_ext/load_error.rb
.