Strange SimpleDelegator behavior

delegation, ruby

Solution

`Delegator` saying:

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.

Okay,so now look at the output,which is to the right of the symbol `# =>`.

require 'delegate'

class Foo < SimpleDelegator
  def meth
    p 'new_meth'
  end
end

class Bar
  def meth
    p 'old_meth'
  end

  def bar_meth
    self.method(:meth)
  end
end

bar = Bar.new # => #<Bar:0x8b31728>
foo = Foo.new(bar)
foo.__getobj__ # => #<Bar:0x8b31728>
foo.bar_meth # => #<Method: Bar#meth>
foo.method(:meth) # => #<Method: Foo#meth>

So when I used the line `foo.method(:meth)`, then output(`#<Method: Foo#meth>`) confirms that whenever you will call `foo.meth`,then `meth` method of the `Foo` class will be called.But the line `foo.bar_meth` outputs(`#<Method: Bar#meth>`) simply saying that inside the method `bar_meth`,if you call `meth` method then, `Bar#meth` will be invoked.

`SimpleDelegator` saying that:

A concrete implementation of Delegator, this class provides the means to delegate all supported method calls to the object passed into the constructor and even to change the object being delegated to at a later time with #setobj.

Yes,in your case `foo` object has been set to `bar` object,by using `#__setobj__`. The output of the line `foo.__getobj__` is showing that.

Problem

Original source