Class: Class

Inherits:
Object show all
Defined in:
lib/active_support/core_ext/duplicable.rb,
lib/active_support/core_ext/class/removal.rb,
lib/active_support/core_ext/class/attribute.rb,
lib/active_support/core_ext/class/attribute_accessors.rb,
lib/active_support/core_ext/class/delegating_attributes.rb,
lib/active_support/core_ext/class/inheritable_attributes.rb

Overview

Allows attributes to be shared within an inheritance hierarchy, but where each descendant gets a copy of their parents’ attributes, instead of just a pointer to the same. This means that the child can add elements to, for example, an array without those additions being shared with either their parent, siblings, or children, which is unlike the regular class-level attributes that are shared across the entire hierarchy.

Constant Summary collapse

EMPTY_INHERITABLE_ATTRIBUTES =

Prevent this constant from being created multiple times

{}.freeze

Instance Method Summary collapse

Instance Method Details

#cattr_accessor(*syms) ⇒ Object 



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# File 'lib/active_support/core_ext/class/attribute_accessors.rb', line 57

def cattr_accessor(*syms)
  cattr_reader(*syms)
  cattr_writer(*syms)
end

#cattr_reader(*syms) ⇒ Object 



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# File 'lib/active_support/core_ext/class/attribute_accessors.rb', line 10

def cattr_reader(*syms)
  options = syms.extract_options!
  syms.each do |sym|
    next if sym.is_a?(Hash)
    class_eval(<<-EOS, __FILE__, __LINE__ + 1)
      unless defined? @@#{sym}
        @@#{sym} = nil
      end

      def self.#{sym}
        @@#{sym}
      end
    EOS

    unless options[:instance_reader] == false
      class_eval(<<-EOS, __FILE__, __LINE__ + 1)
        def #{sym}
          @@#{sym}
        end
      EOS
    end
  end
end

#cattr_writer(*syms) ⇒ Object 



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# File 'lib/active_support/core_ext/class/attribute_accessors.rb', line 34

def cattr_writer(*syms)
  options = syms.extract_options!
  syms.each do |sym|
    class_eval(<<-EOS, __FILE__, __LINE__ + 1)
      unless defined? @@#{sym}
        @@#{sym} = nil
      end

      def self.#{sym}=(obj)
        @@#{sym} = obj
      end
    EOS

    unless options[:instance_writer] == false
      class_eval(<<-EOS, __FILE__, __LINE__ + 1)
        def #{sym}=(obj)
          @@#{sym} = obj
        end
      EOS
    end
  end
end

#class_attribute(*attrs) ⇒ Object

Declare a class-level attribute whose value is inheritable and overwritable by subclasses:

class Base
  class_attribute :setting
end

class Subclass < Base
end

Base.setting = true
Subclass.setting            # => true
Subclass.setting = false
Subclass.setting            # => false
Base.setting                # => true

This matches normal Ruby method inheritance: think of writing an attribute on a subclass as overriding the reader method.

For convenience, a query method is defined as well:

Subclass.setting?           # => false

Instances may overwrite the class value in the same way:

Base.setting = true
object = Base.new
object.setting          # => true
object.setting = false
object.setting          # => false
Base.setting            # => true

To opt out of the instance writer method, pass :instance_writer => false.

object.setting = false  # => NoMethodError



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# File 'lib/active_support/core_ext/class/attribute.rb', line 40

def class_attribute(*attrs)
  instance_writer = !attrs.last.is_a?(Hash) || attrs.pop[:instance_writer]

  attrs.each do |name|
    class_eval <<-RUBY, __FILE__, __LINE__ + 1
      def self.#{name}() nil end
      def self.#{name}?() !!#{name} end

      def self.#{name}=(val)
        singleton_class.class_eval do
          remove_possible_method(:#{name})
          define_method(:#{name}) { val }
        end
      end

      def #{name}
        defined?(@#{name}) ? @#{name} : singleton_class.#{name}
      end

      def #{name}?
        !!#{name}
      end
    RUBY

    attr_writer name if instance_writer
  end
end

#class_inheritable_accessor(*syms) ⇒ Object 



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# File 'lib/active_support/core_ext/class/inheritable_attributes.rb', line 76

def class_inheritable_accessor(*syms)
  class_inheritable_reader(*syms)
  class_inheritable_writer(*syms)
end

#class_inheritable_array(*syms) ⇒ Object 



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# File 'lib/active_support/core_ext/class/inheritable_attributes.rb', line 81

def class_inheritable_array(*syms)
  class_inheritable_reader(*syms)
  class_inheritable_array_writer(*syms)
end

#class_inheritable_array_writer(*syms) ⇒ Object 



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# File 'lib/active_support/core_ext/class/inheritable_attributes.rb', line 42

def class_inheritable_array_writer(*syms)
  options = syms.extract_options!
  syms.each do |sym|
    class_eval <<-EOS
      def self.#{sym}=(obj)                          # def self.levels=(obj)
        write_inheritable_array(:#{sym}, obj)        #   write_inheritable_array(:levels, obj)
      end                                            # end
                                                     #
      #{"                                            #
      def #{sym}=(obj)                               # def levels=(obj)
        self.class.#{sym} = obj                      #   self.class.levels = obj
      end                                            # end
      " unless options[:instance_writer] == false }  # # the writer above is generated unless options[:instance_writer] == false
    EOS
  end
end

#class_inheritable_hash(*syms) ⇒ Object 



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# File 'lib/active_support/core_ext/class/inheritable_attributes.rb', line 86

def class_inheritable_hash(*syms)
  class_inheritable_reader(*syms)
  class_inheritable_hash_writer(*syms)
end

#class_inheritable_hash_writer(*syms) ⇒ Object 



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# File 'lib/active_support/core_ext/class/inheritable_attributes.rb', line 59

def class_inheritable_hash_writer(*syms)
  options = syms.extract_options!
  syms.each do |sym|
    class_eval <<-EOS
      def self.#{sym}=(obj)                          # def self.nicknames=(obj)
        write_inheritable_hash(:#{sym}, obj)         #   write_inheritable_hash(:nicknames, obj)
      end                                            # end
                                                     #
      #{"                                            #
      def #{sym}=(obj)                               # def nicknames=(obj)
        self.class.#{sym} = obj                      #   self.class.nicknames = obj
      end                                            # end
      " unless options[:instance_writer] == false }  # # the writer above is generated unless options[:instance_writer] == false
    EOS
  end
end

#class_inheritable_reader(*syms) ⇒ Object

:nodoc:



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# File 'lib/active_support/core_ext/class/inheritable_attributes.rb', line 10

def class_inheritable_reader(*syms)
  syms.each do |sym|
    next if sym.is_a?(Hash)
    class_eval <<-EOS
      def self.#{sym}                        # def self.before_add_for_comments
        read_inheritable_attribute(:#{sym})  #   read_inheritable_attribute(:before_add_for_comments)
      end                                    # end
                                             #
      def #{sym}                             # def before_add_for_comments
        self.class.#{sym}                    #   self.class.before_add_for_comments
      end                                    # end
    EOS
  end
end

#class_inheritable_writer(*syms) ⇒ Object 



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# File 'lib/active_support/core_ext/class/inheritable_attributes.rb', line 25

def class_inheritable_writer(*syms)
  options = syms.extract_options!
  syms.each do |sym|
    class_eval <<-EOS
      def self.#{sym}=(obj)                          # def self.color=(obj)
        write_inheritable_attribute(:#{sym}, obj)    #   write_inheritable_attribute(:color, obj)
      end                                            # end
                                                     #
      #{"                                            #
      def #{sym}=(obj)                               # def color=(obj)
        self.class.#{sym} = obj                      #   self.class.color = obj
      end                                            # end
      " unless options[:instance_writer] == false }  # # the writer above is generated unless options[:instance_writer] == false
    EOS
  end
end

#duplicable? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/active_support/core_ext/duplicable.rb', line 40

def duplicable?
  false
end

#inheritable_attributes ⇒ Object 



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# File 'lib/active_support/core_ext/class/inheritable_attributes.rb', line 91

def inheritable_attributes
  @inheritable_attributes ||= EMPTY_INHERITABLE_ATTRIBUTES
end

#read_inheritable_attribute(key) ⇒ Object 



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# File 'lib/active_support/core_ext/class/inheritable_attributes.rb', line 112

def read_inheritable_attribute(key)
  inheritable_attributes[key]
end

#remove_class(*klasses) ⇒ Object

Removes the classes in klasses from their parent module.

Ordinary classes belong to some module via a constant. This method computes that constant name from the class name and removes it from the module it belongs to.

Object.remove_class(Integer) # => [Integer]
Integer                      # => NameError: uninitialized constant Integer

Take into account that in general the class object could be still stored somewhere else.

i = Integer                  # => Integer
Object.remove_class(Integer) # => [Integer]
Integer                      # => NameError: uninitialized constant Integer
i.subclasses                 # => ["Bignum", "Fixnum"]
Fixnum.superclass            # => Integer



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# File 'lib/active_support/core_ext/class/removal.rb', line 36

def remove_class(*klasses)
  klasses.flatten.each do |klass|
    # Skip this class if there is nothing bound to this name
    next unless defined?(klass.name)
    
    basename = klass.to_s.split("::").last
    parent = klass.parent
    
    # Skip this class if it does not match the current one bound to this name
    next unless parent.const_defined?(basename) && klass = parent.const_get(basename)

    parent.instance_eval { remove_const basename } unless parent == klass
  end
end

#remove_subclasses ⇒ Object

Unassociates the class with its subclasses and removes the subclasses themselves.

Integer.remove_subclasses # => [Bignum, Fixnum]
Fixnum                    # => NameError: uninitialized constant Fixnum



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# File 'lib/active_support/core_ext/class/removal.rb', line 8

def remove_subclasses
  Object.remove_subclasses_of(self)
end

#reset_inheritable_attributes ⇒ Object 



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# File 'lib/active_support/core_ext/class/inheritable_attributes.rb', line 116

def reset_inheritable_attributes
  @inheritable_attributes = EMPTY_INHERITABLE_ATTRIBUTES
end

#subclasses ⇒ Object

Returns an array with the names of the subclasses of self as strings.

Integer.subclasses # => ["Bignum", "Fixnum"]



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# File 'lib/active_support/core_ext/class/removal.rb', line 15

def subclasses
  Object.subclasses_of(self).map { |o| o.to_s }
end

#superclass_delegating_accessor(*names) ⇒ Object 



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# File 'lib/active_support/core_ext/class/delegating_attributes.rb', line 43

def superclass_delegating_accessor(*names)
  superclass_delegating_reader(*names)
  superclass_delegating_writer(*names)
end

#superclass_delegating_reader(*names) ⇒ Object 



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# File 'lib/active_support/core_ext/class/delegating_attributes.rb', line 8

def superclass_delegating_reader(*names)
  class_name_to_stop_searching_on = self.superclass.name.blank? ? "Object" : self.superclass.name
  names.each do |name|
    class_eval <<-EOS
    def self.#{name}                                            # def self.only_reader
      if defined?(@#{name})                                     #   if defined?(@only_reader)
        @#{name}                                                #     @only_reader
      elsif superclass < #{class_name_to_stop_searching_on} &&  #   elsif superclass < Object &&
            superclass.respond_to?(:#{name})                    #         superclass.respond_to?(:only_reader)
        superclass.#{name}                                      #     superclass.only_reader
      end                                                       #   end
    end                                                         # end
    def #{name}                                                 # def only_reader
      self.class.#{name}                                        #   self.class.only_reader
    end                                                         # end
    def self.#{name}?                                           # def self.only_reader?
      !!#{name}                                                 #   !!only_reader
    end                                                         # end
    def #{name}?                                                # def only_reader?
      !!#{name}                                                 #   !!only_reader
    end                                                         # end
    EOS
  end
end

#superclass_delegating_writer(*names) ⇒ Object 



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# File 'lib/active_support/core_ext/class/delegating_attributes.rb', line 33

def superclass_delegating_writer(*names)
  names.each do |name|
    class_eval <<-EOS
      def self.#{name}=(value)  # def self.only_writer=(value)
        @#{name} = value        #   @only_writer = value
      end                       # end
    EOS
  end
end

#write_inheritable_array(key, elements) ⇒ Object 



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# File 'lib/active_support/core_ext/class/inheritable_attributes.rb', line 102

def write_inheritable_array(key, elements)
  write_inheritable_attribute(key, []) if read_inheritable_attribute(key).nil?
  write_inheritable_attribute(key, read_inheritable_attribute(key) + elements)
end

#write_inheritable_attribute(key, value) ⇒ Object 



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# File 'lib/active_support/core_ext/class/inheritable_attributes.rb', line 95

def write_inheritable_attribute(key, value)
  if inheritable_attributes.equal?(EMPTY_INHERITABLE_ATTRIBUTES)
    @inheritable_attributes = {}
  end
  inheritable_attributes[key] = value
end

#write_inheritable_hash(key, hash) ⇒ Object 



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# File 'lib/active_support/core_ext/class/inheritable_attributes.rb', line 107

def write_inheritable_hash(key, hash)
  write_inheritable_attribute(key, {}) if read_inheritable_attribute(key).nil?
  write_inheritable_attribute(key, read_inheritable_attribute(key).merge(hash))
end