From: Justin Collins <collinsj@...>
Date: 2006-05-14T07:48:11+09:00
Subject: Re: Using alias_method in mixin module

Daniel Berger wrote:
> Justin Collins wrote:
>> Hi all,
>>
>> I have a mixin module that needs to redefine a particular method if 
>> it already exists and retain a reference to it for later use. This is 
>> what I came up with:
>>
>> module Example
>>
>>        def Example.included(klass)
>>                if klass.instance_methods.include? "look_inside"
>>                        klass.instance_eval { alias_method 
>> :old_look_inside, :look_inside }
>>                        klass.send(:define_method, :look_inside) { 
>> |event|
>>                            #use old_look_inside in here
>>                        }
>>                end
>>        end
>>
>> end
>>
>>
>> Is there a better/different way of doing this? (This works, I'm just 
>> curious).
>
> I'd say you should alias the module's method, not the original class' 
> method, because otherwise class hierarchy issues could get confusing. 
> How should a subclass behave, for example?
>
> Anyway, I wrote the 'use' package specifically to deal with this 
> situation:
>
> class Foo
>    include Example, :alias => {:look_inside, :example_look_inside}
> end
>
> Your other option is to adopt a simple naming convention for your 
> modules, where all methods from the Example module start with 
> 'example_' (for example), and avoid the entire issue altogether.
>
> Regards,
>
> Dan
Hi Dan,

The module should only provide this new method if the class that is 
including it has it. In other words, I need to wrap the method call in 
some logic when this module is included. The module does not provide the 
method if the class that mixes in the module does not have the existing 
method. I haven't seen a way of doing the alias in the module that will 
accomplish this. I'm not sure using a naming convention would help in 
this particular case, because it should be transparent to any outside 
calls to the method.
As far as subclassing (subclassing the class which mixes in the 
module?), it should retain the behavior provided in the module.

Thanks.

-Justin