From: "David A. Black" <dblack@...>
Date: 2005-04-14T10:09:52+09:00
Subject: Re: Mocking out a class object

Hi --

On Thu, 14 Apr 2005, Avdi Grimm wrote:

>
> Okay, I'm trying to mock up a class object.  It needs to do two
> things:
>
> 1. Respond to #new with a object *I* provide, rather than a new
>   instance of the class; and
> 2. Contain a constant, such that code containing 'MyMockClass::FOO'
>   will work.
[...]
> I'm wondering, though, is there a way to do this inline with
> metaprogramming, and avoid defining the set_instance method?  I've
> tried something like this:
>
>    my_instance=...
>
>    Class.new :MyMockClass {
>        const_set :FOO, "some value"
>        define_method(:new) do |*|
>            return my_instance
>        end
>    }
>
> But that doesn't work, because the define_method is creating an
> instance method, not a class method.  I've also tried to use a regular
> old object, instead of a class object, but then the constant (FOO)
> doesn't work.  Any ideas?

You're actually dealing with two classes: MyMockClass, and
MyMockClass's singleton class.  So you would probably want to do
something like this:

     # This is to make it look nicer (as per the
     # pending RCR :-)
     module Kernel
       def singleton_class
         class << self; self; end
       end
     end

     my_instance = ""

     MyMockClass = Class.new {
       self::FOO = "some value"
       singleton_class.class_eval {
         define_method(:new) {|*| my_instance}
       }
     }

     p MyMockClass::FOO    # "some value"
     p MyMockClass.new     # ""


David

-- 
David A. Black
dblack@wobblini.net