A duck-type assistant method. For example, Active Support extends Date to define an acts_like_date? method, and extends Time to define acts_like_time?. As a result, we can do x.acts_like?(:time) and x.acts_like?(:date) to do duck-type-safe comparisons, since classes that we want to act like Time simply need to define an acts_like_time? method.

# File activesupport/lib/active_support/core_ext/object/acts_like.rb, line 7
def acts_like?(duck)
  respond_to? :"acts_like_#{duck}?"
end

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

This simplifies

address.nil? || address.empty?

to

address.blank?

@return [true, false]

# File activesupport/lib/active_support/core_ext/object/blank.rb, line 15
def blank?
  respond_to?(:empty?) ? !!empty? : !self
end

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

# File activesupport/lib/active_support/core_ext/object/deep_dup.rb, line 13
def deep_dup
  duplicable? ? dup : self
end

Can you safely dup this object?

False for nil, false, true, symbol, and number objects; true otherwise.

# File activesupport/lib/active_support/core_ext/object/duplicable.rb, line 24
def duplicable?
  true
end

Returns true if this object is included in the argument. Argument must be any object which responds to #include?. Usage:

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

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

# File activesupport/lib/active_support/core_ext/object/inclusion.rb, line 10
def in?(another_object)
  another_object.include?(self)
rescue NoMethodError
  raise ArgumentError.new("The parameter passed to #in? must respond to #include?")
end

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}

# File activesupport/lib/active_support/core_ext/object/instance_variables.rb, line 12
def instance_values
  Hash[instance_variables.map { |name| [name[1..-1], instance_variable_get(name)] }]
end

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"]

# File activesupport/lib/active_support/core_ext/object/instance_variables.rb, line 25
def instance_variable_names
  instance_variables.map { |var| var.to_s }
end

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]

# File activesupport/lib/active_support/core_ext/object/blank.rb, line 42
def presence
  self if present?
end

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]

# File activesupport/lib/active_support/core_ext/object/inclusion.rb, line 24
def presence_in(another_object)
  self.in?(another_object) ? self : nil
end

An object is present if it's not blank.

@return [true, false]

# File activesupport/lib/active_support/core_ext/object/blank.rb, line 22
def present?
  !blank?
end

Alias of to_s.

# File activesupport/lib/active_support/core_ext/object/to_query.rb, line 3
def to_param
  to_s
end

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

# File activesupport/lib/active_support/core_ext/object/to_query.rb, line 9
def to_query(key)
  require 'cgi' unless defined?(CGI) && defined?(CGI::escape)
  "#{CGI.escape(key.to_param)}=#{CGI.escape(to_param.to_s)}"
end

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 ? @person.name : 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 otherwise.

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

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

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. For example, using try with SimpleDelegator will delegate try to the target instead of calling it on delegator itself.

# File activesupport/lib/active_support/core_ext/object/try.rb, line 41
def try(*a, &b)
  if a.empty? && block_given?
    yield self
  else
    public_send(*a, &b) if respond_to?(a.first)
  end
end

Same as try, but will raise a NoMethodError exception if the receiving is not nil and does not implement the tried method.

# File activesupport/lib/active_support/core_ext/object/try.rb, line 51
def try!(*a, &b)
  if a.empty? && block_given?
    yield self
  else
    public_send(*a, &b)
  end
end

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 options hash 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

with_options can also be nested since the call is forwarded to its receiver. Each nesting level will merge inherited defaults in addition to their own.

# File activesupport/lib/active_support/core_ext/object/with_options.rb, line 39
def with_options(options)
  yield ActiveSupport::OptionMerger.new(self, options)
end