From: Logan Capaldo <logancapaldo@...>
Date: 2006-07-12T14:15:19+09:00
Subject: Re: alias new???


On Jul 12, 2006, at 1:01 AM, ara.t.howard@noaa.gov wrote:

> On Wed, 12 Jul 2006, Logan Capaldo wrote:
>
>> Couple of things
>> 1) alias_method gets executed at "compile" time. This means that  
>> it will try to alias MagicWithNew.
>>
>> 2) This is ok because you dont want to use alias's in this case.  
>> Since #new is almost never overriden (it's usually #initialize.  
>> Incidentally are you sure you don't want to define #initialize  
>> instead?) it's pretty much guaranteed that you class is using the  
>> original implementation in Class.
>> so we can use inheritance and super
>>
>>
>> module MagicWithNew
>>  def new(*args, &block)
>>    if some_condition
>>       do_special_stuff
>
>   fails to initialize object!  you need the old 'new' here.  or super.
>
Well he did say "special stuff". He only needs old new or super there  
if he plans on initializing the object ;)

>
>>    else
>>       super
>>    end
>>  end
>> end
>>
>> class MyClass
>>  extend MagicWithNew # note #extend,  not #include
>> end
>
> here is an example of a fairly robust pattern
>
>   harp:~ > cat a.rb
>   module M
>     ClassMethods = lambda do
>       alias_method '__new__', 'new'  # correct alias of new
>
>       def new *a, &b
>         obj = __new__(*a, &b)
>       #
>       # do anything you want with obj here based on any condition.   
> this is just
>       # an example.
>       #
>         class << obj
>           def answer() 42 end
>         end
>         obj
>       end
>     end
>
>     def self.included other
>       meta =
>         class << other
>           self
>         end
>       meta.module_eval &ClassMethods
>       super
>     end
>   end
>
>   class C
>     include M
>   end
>
>   p C.new.answer
>
>   harp:~ > ruby a.rb
>   42
>
>
> regards.
>
> -a
> -- 
> suffering increases your inner strength.  also, the wishing for  
> suffering
> makes the suffering disappear.
> - h.h. the 14th dali lama
>