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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.

Methods
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Constants

VERSION = "0.3.1"
 

Class Public methods

new(obj)

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

Source: show | on GitHub 

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

Instance Public methods

!()

Delegates ! to the _getobj_

Source: show | on GitHub 

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

!=(obj)

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

Source: show | on GitHub 

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

==(obj)

Returns true if two objects are considered of equal value.

Source: show | on GitHub 

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

__getobj__()

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

Source: show | on GitHub 

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

__raise__

Alias for: raise

__setobj__(obj)

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

Source: show | on GitHub 

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

eql?(obj)

Returns true if two objects are considered of equal value.

Source: show | on GitHub 

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

freeze()

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

Source: show | on GitHub 

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

marshal_dump()

Serialization support for the object returned by _getobj_.

Source: show | on GitHub 

# File ruby/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)

Reinitializes delegation from a serialized object.

Source: show | on GitHub 

# File ruby/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)

Source: show | on GitHub 

# File ruby/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)

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

Source: show | on GitHub 

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

protected_methods(all=true)

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

Source: show | on GitHub 

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

public_methods(all=true)

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

Source: show | on GitHub 

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

raise

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

Also aliased as: __raise__

Source: show | on GitHub 

# File ruby/lib/delegate.rb, line 66

respond_to_missing?(m, include_private)

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

Source: show | on GitHub 

# File ruby/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