From: Kevin Mahler <kevin.mahler@...>
Date: 2011-04-17T00:32:22+09:00
Subject: Re: What do you do when you need to attach data to an object instance?

7stud -- wrote in post #993115:
> Kevin Mahler wrote in post #992907:
>>
>>   def extend_accessor(obj, name)
>>     obj.singleton_class.module_eval { attr_accessor name }
>>     obj
>>   end
>>
>
> Hey, now.  obj.singleton_class is a class, so how about using the
> synonym class_eval():
>
>       obj.singleton_class.class_eval { attr_accessor name }

A class is a module, but a module is not a class.

  Class.new.is_a? Module #=>true
  Module.new.is_a? Class #=>false

Because module_eval and class_eval are aliases, class_eval can be
called on a module, a situation which is at worst wrong and at best
confusing. module_eval can never be wrong or confusing. Not a hard
choice.

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