Provides a way to check whether some class acts like some other class based on the existence of an appropriately-named marker method.

A class that provides the same interface as SomeClass may define a marker method named acts_like_some_class? to signal its compatibility to callers of acts_like?(:some_class).

For example, Active Support extends Date to define an acts_like_date? method, and extends Time to define acts_like_time?. As a result, developers can call x.acts_like?(:time) and x.acts_like?(:date) to test duck-type compatibility, and classes that are able to act like Time can also define an acts_like_time? method to interoperate.

Note that the marker method is only expected to exist. It isn’t called, so its body or return value are irrelevant.

Example: A class that provides the same interface as String

This class may define:

class Stringish def acts_like_string? end end 

Then client code can query for duck-type-safeness this way:

Stringish.new.acts_like?(:string) # => true 

An object is blank if it’s false, empty, or a whitespace string. For example, nil, ”, ‘ ’, [], {}, and false are all blank.

This simplifies

!address || address.empty? 

to

address.blank? 

@return [true, false]

Returns a deep copy of object if it’s duplicable. If it’s not duplicable, returns self.

object = Object.new dup = object.deep_dup dup.instance_variable_set(:@a, 1) object.instance_variable_defined?(:@a) # => false dup.instance_variable_defined?(:@a) # => true 

Can you safely dup this object?

False for method objects; true otherwise.

Returns true if this object is included in the argument.

When argument is a Range, cover? is used to properly handle inclusion check within open ranges. Otherwise, argument must be any object which responds to include?. Usage:

characters = ["Konata", "Kagami", "Tsukasa"] "Konata".in?(characters) # => true 

For non Range arguments, this will throw an ArgumentError if the argument doesn’t respond to include?.

Returns a hash with string keys that maps instance variable names without “@” to their corresponding values.

class C def initialize(x, y) @x, @y = x, y end end C.new(0, 1).instance_values # => {"x" => 0, "y" => 1} 

Returns an array of instance variable names as strings including “@”.

class C def initialize(x, y) @x, @y = x, y end end C.new(0, 1).instance_variable_names # => ["@y", "@x"] 

Returns the receiver if it’s present otherwise returns nil. object.presence is equivalent to

object.present? ? object : nil 

For example, something like

state = params[:state] if params[:state].present? country = params[:country] if params[:country].present? region = state || country || 'US' 

becomes

region = params[:state].presence || params[:country].presence || 'US' 

@return [Object]

Returns the receiver if it’s included in the argument otherwise returns nil. Argument must be any object which responds to include?. Usage:

params[:bucket_type].presence_in %w( project calendar ) 

This will throw an ArgumentError if the argument doesn’t respond to include?.

@return [Object]

An object is present if it’s not blank.

@return [true, false]

Alias of to_s.

Converts an object into a string suitable for use as a URL query string, using the given key as the param name.

Invokes the public method whose name goes as first argument just like public_send does, except that if the receiver does not respond to it the call returns nil rather than raising an exception.

This method is defined to be able to write

@person.try(:name) 

instead of

@person.name if @person 

try calls can be chained:

@person.try(:spouse).try(:name) 

instead of

@person.spouse.name if @person && @person.spouse 

try will also return nil if the receiver does not respond to the method:

@person.try(:non_existing_method) # => nil 

instead of

@person.non_existing_method if @person.respond_to?(:non_existing_method) # => nil 

try returns nil when called on nil regardless of whether it responds to the method:

nil.try(:to_i) # => nil, rather than 0 

Arguments and blocks are forwarded to the method if invoked:

@posts.try(:each_slice, 2) do |a, b| ... end 

The number of arguments in the signature must match. If the object responds to the method the call is attempted and ArgumentError is still raised in case of argument mismatch.

If try is called without arguments it yields the receiver to a given block unless it is nil:

@person.try do |p| ... end 

You can also call try with a block without accepting an argument, and the block will be instance_eval’ed instead:

@person.try { upcase.truncate(50) } 

Please also note that try is defined on Object. Therefore, it won’t work with instances of classes that do not have Object among their ancestors, like direct subclasses of BasicObject.

Same as try, but raises a NoMethodError exception if the receiver is not nil and does not implement the tried method.

"a".try!(:upcase) # => "A" nil.try!(:upcase) # => nil 123.try!(:upcase) # => NoMethodError: undefined method `upcase' for 123:Integer 

Set and restore public attributes around a block.

client.timeout # => 5 client.with(timeout: 1) do |c| c.timeout # => 1 end client.timeout # => 5 

The receiver is yielded to the provided block.

This method is a shorthand for the common begin/ensure pattern:

old_value = object.attribute begin object.attribute = new_value # do things ensure object.attribute = old_value end 

It can be used on any object as long as both the reader and writer methods are public.

An elegant way to factor duplication out of options passed to a series of method calls. Each method called in the block, with the block variable as the receiver, will have its options merged with the default optionsHash or Hash-like object provided. Each method called on the block variable must take an options hash as its final argument.

Without with_options, this code contains duplication:

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 

Using with_options, we can remove the duplication:

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 

It can also be used with an explicit receiver:

I18n.with_options locale: user.locale, scope: 'newsletter' do |i18n| subject i18n.t :subject body i18n.t :body, user_name: user.name end 

When you don’t pass an explicit receiver, it executes the whole block in merging options context:

class Account < ActiveRecord::Base with_options dependent: :destroy do has_many :customers has_many :products has_many :invoices has_many :expenses end end 

with_options can also be nested since the call is forwarded to its receiver.

NOTE: Each nesting level will merge inherited defaults in addition to their own.

class Post < ActiveRecord::Base with_options if: :persisted?, length: { minimum: 50 } do validates :content, if: -> { content.present? } end end 

The code is equivalent to:

validates :content, length: { minimum: 50 }, if: -> { content.present? } 

Hence the inherited default for if key is ignored.

NOTE: You cannot call class methods implicitly inside of with_options. You can access these methods using the class name instead:

class Phone < ActiveRecord::Base enum :phone_number_type, { home: 0, office: 1, mobile: 2 } with_options presence: true do validates :phone_number_type, inclusion: { in: Phone.phone_number_types.keys } end end 

When the block argument is omitted, the decorated Object instance is returned:

module MyStyledHelpers def styled with_options style: "color: red;" end end styled.link_to "I'm red", "/" # => <a href="/" style="color: red;">I'm red</a> styled.button_tag "I'm red too!" # => <button style="color: red;">I'm red too!</button>