From: dblack@...
Date: 2007-05-28T08:07:27+09:00
Subject: Re: Tricky problem with ===

Hi --

On Sun, 27 May 2007, Erwin Abbott wrote:

> On 5/27/07, Robert Klemme wrote:
>> Erwin, are you aware of delegate?
>
> Yes, but it's not transparent as I'd like. I don't want the delegating
> class to answer methods like class and is_a? for example. It also
> doesn't work when trying to distinguish the class with a case
> construct.
>
> On 27.05.2007 07:04, Morton Goldberg wrote:
>> What I see when I evaluate your code is:
>>
>>    x.class # => String
>>    x.size  # => 14
>
> My mistake, I had an array to begin with and didn't remember to change
> the results to match when I changed it to a string.
>
>> A better solution would be to use the second form of "case" to have more
>> control over the test
>> 
>> case
>>    when Array == x.class
>>    when String == x.class
>> end
>
> That's not bad. I like it... and it's a little more explicit, too. I
> didn't know you could use case that way, that seems pretty useful.
>
>> Viewing this more abstract: maybe case isn't even the right thing to do.
>>   We would have to know more about what the OP is trying to accomplish.
>
> Well the idea is to wrap an object with this proxy class and not mess
> up any code that doesn't know about it... it should seem completely
> transparent. It gives you a separate namespace for methods and
> instance variables, so you don't have to worry about redefining those
> with a mixin or singleton method, but you can still specialize some
> object by wrapping it.
>
>> I think using case statements to distinguish the class of an object is
>> kind of ugly under any circumstances.
>
> I think it works pretty well, but I'd like to know what you prefer
> instead. I realize distinguishing objects by class is not encouraged,
> but I find myself needing it often, for better or worse.

But you're running aground on exactly why it isn't encouraged: namely,
it doesn't give you definitive information about the object's behavior
or interface.  Are you sure a mixin wouldn't make more sense?


David

-- 
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