class Delegator - Documentation for Ruby 4.1
Description: class Delegator: This library provides three different ways to delegate method calls to an object. The easiest to use is SimpleDelegator.
Keywords: ruby,class,Delegator

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# class Delegator

This library provides three different ways to delegate method calls to an object. The easiest to use is `SimpleDelegator`. Pass an object to the constructor and all methods supported by the object will be delegated. This object can be changed later.

Going a step further, the top level DelegateClass method allows you to easily setup delegation through class inheritance. This is considerably more flexible and thus probably the most common use for this library.

Finally, if you need full control over the delegation scheme, you can inherit from the abstract class `Delegator` and customize as needed. (If you find yourself needing this control, have a look at `Forwardable` which is also in the standard library. It may suit your needs better.)

SimpleDelegator’s implementation serves as a nice example of the use of Delegator:

    require 'delegate'

    class SimpleDelegator < Delegator
      def __getobj__
        @delegate_sd_obj # return object we are delegating to, required
      end

      def __setobj__(obj)
        @delegate_sd_obj = obj # change delegation object,
                               # a feature we're providing
      end
    end

## Notes

Be advised, RDoc will not detect delegated methods.

### Constants

VERSION

  The version string

### Public Class Methods

new (obj)
Source

    # File lib/delegate.rb, line 76
    def initialize(obj)
      __setobj__(obj)
    end

Pass in the obj to delegate method calls to. All methods supported by obj will be delegated to.

### Public Instance Methods

! ()
Source

    # File lib/delegate.rb, line 181
    def !
      !__getobj__
    end

Delegates ! to the `__getobj__`

!= (obj)
Source

    # File lib/delegate.rb, line 165
    def !=(obj)
      return false if obj.equal?(self)
      __getobj__ != obj
    end

Returns true if two objects are not considered of equal value.

== (obj)
Source

    # File lib/delegate.rb, line 157
    def ==(obj)
      return true if obj.equal?(self)
      self.__getobj__ == obj
    end

Returns true if two objects are considered of equal value.

__getobj__ ()
Source

    # File lib/delegate.rb, line 189
    def __getobj__
      __raise__ ::NotImplementedError, "need to define '__getobj__'"
    end

This method must be overridden by subclasses and should return the object method calls are being delegated to.

__setobj__ (obj)
Source

    # File lib/delegate.rb, line 197
    def __setobj__(obj)
      __raise__ ::NotImplementedError, "need to define '__setobj__'"
    end

This method must be overridden by subclasses and change the object delegate to obj.

eql? (obj)
Source

    # File lib/delegate.rb, line 173
    def eql?(obj)
      return true if obj.equal?(self)
      obj.eql?(__getobj__)
    end

Returns true if two objects are considered of equal value.

freeze ()
Source

    # File lib/delegate.rb, line 238
    def freeze
      __getobj__.freeze
      super()
    end

Freeze both the object returned by `__getobj__` and self.

Calls superclass method
marshal_dump ()
Source

    # File lib/delegate.rb, line 204
    def marshal_dump
      ivars = instance_variables.reject {|var| /\A@delegate_/ =~ var}
      [
        :__v2__,
        ivars, ivars.map {|var| instance_variable_get(var)},
        __getobj__
      ]
    end

Serialization support for the object returned by `__getobj__`.

marshal_load (data)
Source

    # File lib/delegate.rb, line 216
    def marshal_load(data)
      version, vars, values, obj = data
      if version == :__v2__
        vars.each_with_index {|var, i| instance_variable_set(var, values[i])}
        __setobj__(obj)
      else
        __setobj__(data)
      end
    end

Reinitializes delegation from a serialized object.

method_missing (m, *args, &block)
Source

    # File lib/delegate.rb, line 83
                   def method_missing(m, *args, &block)
      r = true
      target = self.__getobj__ {r = false}

      if r && target_respond_to?(target, m, false)
        target.__send__(m, *args, &block)
      elsif ::Kernel.method_defined?(m) || ::Kernel.private_method_defined?(m)
        ::Kernel.instance_method(m).bind_call(self, *args, &block)
      else
        super(m, *args, &block)
      end
    end

Handles the magic of delegation through `__getobj__`.

Calls superclass method `BasicObject#method_missing`
methods (all=true)
Source

    # File lib/delegate.rb, line 132
    def methods(all=true)
      __getobj__.methods(all) | super
    end

Returns the methods available to this delegate object as the union of this object’s and `__getobj__` methods.

Calls superclass method
protected_methods (all=true)
Source

    # File lib/delegate.rb, line 148
    def protected_methods(all=true)
      __getobj__.protected_methods(all) | super
    end

Returns the methods available to this delegate object as the union of this object’s and `__getobj__` protected methods.

Calls superclass method
public_methods (all=true)
Source

    # File lib/delegate.rb, line 140
    def public_methods(all=true)
      __getobj__.public_methods(all) | super
    end

Returns the methods available to this delegate object as the union of this object’s and `__getobj__` public methods.

Calls superclass method
raise ()
Source

    # File lib/delegate.rb, line 67

Use #__raise__ if your `Delegator` does not have a object to delegate the `raise` method call.

respond_to_missing? (m, include_private)
Source

    # File lib/delegate.rb, line 100
    def respond_to_missing?(m, include_private)
      r = true
      target = self.__getobj__ {r = false}
      r &&= target_respond_to?(target, m, include_private)
      if r && include_private && !target_respond_to?(target, m, false)
        warn "delegator does not forward private method \##{m}", uplevel: 3
        return false
      end
      r
    end

Checks for a method provided by this the delegate object by forwarding the call through `__getobj__`.

### Private Instance Methods

target_respond_to? (target, m, include_private)
Source

    # File lib/delegate.rb, line 115
            def target_respond_to?(target, m, include_private)
      case target
      when Object
        target.respond_to?(m, include_private)
      else
        if KERNEL_RESPOND_TO.bind_call(target, :respond_to?)
          target.respond_to?(m, include_private)
        else
          KERNEL_RESPOND_TO.bind_call(target, m, include_private)
        end
      end
    end

Handle `BasicObject` instances