Class: Object

Inherits:
BasicObject
Defined in:
activesupport/lib/active_support/core_ext/object/duplicable.rb,
activesupport/lib/active_support/core_ext/object/try.rb,
activesupport/lib/active_support/core_ext/object/json.rb,
activesupport/lib/active_support/core_ext/object/blank.rb,
activesupport/lib/active_support/core_ext/object/to_query.rb,
activesupport/lib/active_support/core_ext/object/deep_dup.rb,
activesupport/lib/active_support/core_ext/object/acts_like.rb,
activesupport/lib/active_support/core_ext/object/inclusion.rb,
activesupport/lib/active_support/core_ext/kernel/agnostics.rb,
activesupport/lib/active_support/core_ext/object/with_options.rb,
activesupport/lib/active_support/core_ext/string/output_safety.rb,
activesupport/lib/active_support/core_ext/object/instance_variables.rb

Overview

– Most objects are cloneable, but not all. For example you can't dup nil:

nil.dup # => TypeError: can't dup NilClass

Classes may signal their instances are not duplicable removing dup/clone or raising exceptions from them. So, to dup an arbitrary object you normally use an optimistic approach and are ready to catch an exception, say:

arbitrary_object.dup rescue object

Rails dups objects in a few critical spots where they are not that arbitrary. That rescue is very expensive (like 40 times slower than a predicate), and it is often triggered.

That's why we hardcode the following cases and check duplicable? instead of using that rescue idiom. ++

Instance Method Summary collapse

Instance Method Details

#`(command) ⇒ Object

Makes backticks behave (somewhat more) similarly on all platforms. On win32 `nonexistent_command` raises Errno::ENOENT; on Unix, the spawned shell prints a message to stderr and sets $?. We emulate Unix on the former but not the latter.



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# File 'activesupport/lib/active_support/core_ext/kernel/agnostics.rb', line 6

def `(command) #:nodoc:
  super
rescue Errno::ENOENT => e
  STDERR.puts "#$0: #{e}"
end

#acts_like?(duck) ⇒ Boolean

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.



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# File 'activesupport/lib/active_support/core_ext/object/acts_like.rb', line 7

def acts_like?(duck)
  respond_to? :acts_like_#{duck}?"
end

#as_json(options = nil) ⇒ Object

:nodoc:



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# File 'activesupport/lib/active_support/core_ext/object/json.rb', line 46

def as_json(options = nil) #:nodoc:
  if respond_to?(:to_hash)
    to_hash.as_json(options)
  else
    instance_values.as_json(options)
  end
end

#blank?true, false

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?


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# File 'activesupport/lib/active_support/core_ext/object/blank.rb', line 16

def blank?
  respond_to?(:empty?) ? !!empty? : !self
end

#deep_dupObject

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


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# File 'activesupport/lib/active_support/core_ext/object/deep_dup.rb', line 13

def deep_dup
  duplicable? ? dup : self
end

#duplicable?Boolean

Can you safely dup this object?

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



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# File 'activesupport/lib/active_support/core_ext/object/duplicable.rb', line 24

def duplicable?
  true
end

#html_safe?Boolean



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# File 'activesupport/lib/active_support/core_ext/string/output_safety.rb', line 124

def html_safe?
  false
end

#in?(another_object) ⇒ Boolean

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?.



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# 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

#instance_valuesObject

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}


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# 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

#instance_variable_namesObject

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"]


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# File 'activesupport/lib/active_support/core_ext/object/instance_variables.rb', line 25

def instance_variable_names
  instance_variables.map(&:to_s)
end

#presenceObject

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'


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# File 'activesupport/lib/active_support/core_ext/object/blank.rb', line 43

def presence
  self if present?
end

#presence_in(another_object) ⇒ 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?.



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# File 'activesupport/lib/active_support/core_ext/object/inclusion.rb', line 24

def presence_in(another_object)
  self.in?(another_object) ? self : nil
end

#present?true, false

An object is present if it's not blank.



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# File 'activesupport/lib/active_support/core_ext/object/blank.rb', line 23

def present?
  !blank?
end

#to_paramObject

Alias of to_s.



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# File 'activesupport/lib/active_support/core_ext/object/to_query.rb', line 5

def to_param
  to_s
end

#to_query(key) ⇒ Object

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



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# File 'activesupport/lib/active_support/core_ext/object/to_query.rb', line 11

def to_query(key)
  "#{CGI.escape(key.to_param)}=#{CGI.escape(to_param.to_s)}"
end

#try(*a, &b) ⇒ Object

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



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# File 'activesupport/lib/active_support/core_ext/object/try.rb', line 62

def try(*a, &b)
  try!(*a, &b) if a.empty? || respond_to?(a.first)
end

#try!(*a, &b) ⇒ Object

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:Fixnum


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# File 'activesupport/lib/active_support/core_ext/object/try.rb', line 72

def try!(*a, &b)
  if a.empty? && block_given?
    if b.arity.zero?
      instance_eval(&b)
    else
      yield self
    end
  else
    public_send(*a, &b)
  end
end

#with_options(options, &block) ⇒ Object

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

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.



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# File 'activesupport/lib/active_support/core_ext/object/with_options.rb', line 65

def with_options(options, &block)
  option_merger = ActiveSupport::OptionMerger.new(self, options)
  block.arity.zero? ? option_merger.instance_eval(&block) : block.call(option_merger)
end