From: ES <ruby-ml@...>
Date: 2005-10-07T03:16:07+09:00
Subject: Re: techniques for module to contribute to initialize() of its including classes

Sean O'Halpin wrote:
> On 10/6/05, ES <ruby-ml@magical-cat.org> wrote:
> 
>>Robert Klemme wrote:
>>
>>>itsme213 wrote:
>>>
>>>
>>>>What are good design techniques for this e.g. if the module adds some
>>>>instance variables to its included class?
>>>>
>>>>module M
>>>> def f
>>>>   @f
>>>> end
>>>> # how to initialize @f ?
>>>>end
>>>>
>>>>class A
>>>> include M
>>>>end
>>>>Thanks.
>>>
>>>
>>>Do it like this and the module initialite will seamlessly integrate into
>>>the class inheritance chain:
>>>
>>>module M
>>>  def initialize(*a,&b)
>>>    super
>>>    @f = 10
>>>  end
>>>end
>>
>>This does not work directly if the class itself defines an #initialize
>>as it will take precedence over the module version.
>>
> 
> It works if you call super from within the class initialize. The
> module is inserted into the inheritance chain before any superclasses.

Huh. Should have known better than to try it in irb :)
It does seem to work fine. Ignore me.

> module M
>   def f
>     @f
>   end
>   # how to initialize @f ?
>   def initialize(*args, &block)
>     puts "in M.initialize"
>     super
>     @f = 10
>   end
> end
> 
> class A
>   def initialize(*args, &block)
>     puts "in A.initialize"
>     super
>   end
> end
> 
> class B < A
>   include M
>   def initialize(*args, &block)
>     puts "in B.initialize"
>     super
>   end
> end
> 
> b = B.new
> p b.f
> 
> __END__
> in B.initialize
> in M.initialize
> in A.initialize
> 10
> 
> Sean

E