class Delegator - Documentation for Ruby 3.2

# 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

KERNEL_RESPOND_TO
VERSION

### Public Class Methods

new(obj) click to toggle source

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

    # File lib/delegate.rb, line 75
    def initialize(obj)
      __setobj__(obj)
    end

### Public Instance Methods

!() click to toggle source

Delegates ! to the _getobj_

    # File lib/delegate.rb, line 180
    def !
      !__getobj__
    end

!=(obj) click to toggle source

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

    # File lib/delegate.rb, line 164
    def !=(obj)
      return false if obj.equal?(self)
      __getobj__ != obj
    end

==(obj) click to toggle source

Returns true if two objects are considered of equal value.

    # File lib/delegate.rb, line 156
    def ==(obj)
      return true if obj.equal?(self)
      self.__getobj__ == obj
    end

__getobj__() click to toggle source

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

    # File lib/delegate.rb, line 188
    def __getobj__
      __raise__ ::NotImplementedError, "need to define `__getobj__'"
    end

__raise__()
Alias for: raise
__setobj__(obj) click to toggle source

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

    # File lib/delegate.rb, line 196
    def __setobj__(obj)
      __raise__ ::NotImplementedError, "need to define `__setobj__'"
    end

eql?(obj) click to toggle source

Returns true if two objects are considered of equal value.

    # File lib/delegate.rb, line 172
    def eql?(obj)
      return true if obj.equal?(self)
      obj.eql?(__getobj__)
    end

freeze() click to toggle source

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

Calls superclass method

    # File lib/delegate.rb, line 237
    def freeze
      __getobj__.freeze
      super()
    end

marshal_dump() click to toggle source

Serialization support for the object returned by _getobj_.

    # File lib/delegate.rb, line 203
    def marshal_dump
      ivars = instance_variables.reject {|var| /\A@delegate_/ =~ var}
      [
        :__v2__,
        ivars, ivars.map {|var| instance_variable_get(var)},
        __getobj__
      ]
    end

marshal_load(data) click to toggle source

Reinitializes delegation from a serialized object.

    # File lib/delegate.rb, line 215
    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

method_missing(m, *args, &block) click to toggle source
Calls superclass method `BasicObject#method_missing`

    # File lib/delegate.rb, line 82
                   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

methods(all=true) click to toggle source

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

Calls superclass method

    # File lib/delegate.rb, line 131
    def methods(all=true)
      __getobj__.methods(all) | super
    end

protected_methods(all=true) click to toggle source

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

Calls superclass method

    # File lib/delegate.rb, line 147
    def protected_methods(all=true)
      __getobj__.protected_methods(all) | super
    end

public_methods(all=true) click to toggle source

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

Calls superclass method

    # File lib/delegate.rb, line 139
    def public_methods(all=true)
      __getobj__.public_methods(all) | super
    end

raise() click to toggle source

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

    # File lib/delegate.rb, line 66

Also aliased as: __raise__
respond_to_missing?(m, include_private) click to toggle source

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

    # File lib/delegate.rb, line 99
    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

### Private Instance Methods

target_respond_to?(target, m, include_private) click to toggle source

Handle `BasicObject` instances

    # File lib/delegate.rb, line 114
            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