Class: Object

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

Returns:

  • (Boolean) 


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# File '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 'lib/active_support/json/encoding.rb', line 147

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

#blank? ⇒ Boolean

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

This simplifies:

if address.nil? || address.empty?

…to:

if address.blank?

Returns:

  • (Boolean) 


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# File 'lib/active_support/core_ext/object/blank.rb', line 14

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

#deep_dup ⇒ Object

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 '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, and number objects; true otherwise.

Returns:

  • (Boolean) 


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

def duplicable?
  true
end

#html_safe? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/active_support/core_ext/string/output_safety.rb', line 72

def html_safe?
  false
end

#in?(*args) ⇒ 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?.

Returns:

  • (Boolean) 


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# File 'lib/active_support/core_ext/object/inclusion.rb', line 12

def in?(*args)
  if args.length > 1
    ActiveSupport::Deprecation.warn "Calling #in? with multiple arguments is" \
      " deprecated, please pass in an object that responds to #include? instead."
    args.include? self
  else
    another_object = args.first
    if another_object.respond_to? :include?
      another_object.include? self
    else
      raise ArgumentError.new 'The single parameter passed to #in? must respond to #include?'
    end
  end
end

#instance_values ⇒ Object

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 '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_names ⇒ Object

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

def instance_variable_names
  instance_variables.map { |var| var.to_s }
end

#presence ⇒ Object

Returns object if it’s present? otherwise returns nil. object.presence is equivalent to object.present? ? object : nil.

This is handy for any representation of objects where blank is the same as not present at all. For example, this simplifies a common check for HTTP POST/query parameters:

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 'lib/active_support/core_ext/object/blank.rb', line 37

def presence
  self if present?
end

#present? ⇒ Boolean

An object is present if it’s not blank?.

Returns:

  • (Boolean) 


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# File 'lib/active_support/core_ext/object/blank.rb', line 19

def present?
  !blank?
end

#to_param ⇒ Object

Alias of to_s.



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# File 'lib/active_support/core_ext/object/to_param.rb', line 3

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.

Note: This method is defined as a default implementation for all Objects for Hash#to_query to work.



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# File 'lib/active_support/core_ext/object/to_query.rb', line 8

def to_query(key)
  require 'cgi' unless defined?(CGI) && defined?(CGI::escape)
  "#{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 ? @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.



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# File '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

#try!(*a, &b) ⇒ Object

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



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# File '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

#with_options(options) {|ActiveSupport::OptionMerger.new(self, options)| ... } ⇒ 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

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.

Yields:



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# File 'lib/active_support/core_ext/object/with_options.rb', line 39

def with_options(options)
  yield ActiveSupport::OptionMerger.new(self, options)
end