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 if the use of Delegator:

class SimpleDelegator < Delegator
  def initialize(obj)
    super                  # pass obj to Delegator constructor, required
    @delegate_sd_obj = obj # store obj for future use
  end

  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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Class Public methods
new(obj)

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

# File lib/delegate.rb, line 69
def initialize(obj)
  __setobj__(obj)
end
Instance Public methods
!()

Delegates ! to the _getobj_

# File lib/delegate.rb, line 152
def !
  !__getobj__
end
!=(obj)

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

# File lib/delegate.rb, line 144
def !=(obj)
  return false if obj.equal?(self)
  __getobj__ != obj
end
==(obj)

Returns true if two objects are considered of equal value.

# File lib/delegate.rb, line 136
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.

# File lib/delegate.rb, line 160
def __getobj__
  __raise__ ::NotImplementedError, "need to define `__getobj__'"
end
__setobj__(obj)

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

# File lib/delegate.rb, line 168
def __setobj__(obj)
  __raise__ ::NotImplementedError, "need to define `__setobj__'"
end
freeze

Freeze both the object returned by _getobj_ and self.

# File lib/delegate.rb, line 230
  
marshal_dump()

Serialization support for the object returned by _getobj_.

# File lib/delegate.rb, line 175
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.

# File lib/delegate.rb, line 187
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)

Handles the magic of delegation through _getobj_.

# File lib/delegate.rb, line 76
def method_missing(m, *args, &block)
  r = true
  target = self.__getobj__ {r = false}
  begin
    if r && target.respond_to?(m)
      target.__send__(m, *args, &block)
    elsif ::Kernel.respond_to?(m, true)
      ::Kernel.instance_method(m).bind(self).(*args, &block)
    else
      super(m, *args, &block)
    end
  ensure
    $@.delete_if {|t| %r"\A#{Regexp.quote(__FILE__)}:(?:#{[__LINE__-7, __LINE__-5, __LINE__-3].join('|')}):"o =~ t} if $@
  end
end
methods(all=true)

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

# File lib/delegate.rb, line 111
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.

# File lib/delegate.rb, line 127
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.

# File lib/delegate.rb, line 119
def public_methods(all=true)
  __getobj__.public_methods(all) | super
end
respond_to_missing?(m, include_private)

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

# File lib/delegate.rb, line 96
def respond_to_missing?(m, include_private)
  r = true
  target = self.__getobj__ {r = false}
  r &&= target.respond_to?(m, include_private)
  if r && include_private && !target.respond_to?(m, false)
    warn "#{caller(3)[0]}: delegator does not forward private method \##{m}"
    return false
  end
  r
end
taint

Taint both the object returned by _getobj_ and self.

# File lib/delegate.rb, line 220
  
trust

Trust both the object returned by _getobj_ and self.

# File lib/delegate.rb, line 210
  
untaint

Untaint both the object returned by _getobj_ and self.

# File lib/delegate.rb, line 225
  
untrust

Untrust both the object returned by _getobj_ and self.

# File lib/delegate.rb, line 215