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Showing content from https://docs.ruby-lang.org/en/master/Delegator.html below:

class Delegator - Documentation for Ruby 3.5

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 
  end

  def __setobj__(obj)
    @delegate_sd_obj = obj 
                           
  end
end

Be advised, RDoc will not detect delegated methods.

KERNEL_RESPOND_TO

VERSION

def initialize(obj)
  __setobj__(obj)
end

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

Delegates ! to the _getobj_

def !=(obj)
  return false if obj.equal?(self)
  __getobj__ != obj
end

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

def ==(obj)
  return true if obj.equal?(self)
  self.__getobj__ == obj
end

Returns true if two objects are considered of equal value.

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.

def __setobj__(obj)
  __raise__ ::NotImplementedError, "need to define '__setobj__'"
end

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

def eql?(obj)
  return true if obj.equal?(self)
  obj.eql?(__getobj__)
end

Returns true if two objects are considered of equal value.

def freeze
  __getobj__.freeze
  super()
end

:method: freeze Freeze both the object returned by _getobj_ and self.

Calls superclass method

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_.

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.

               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

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

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

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

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_.

        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

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