From: Jim Weirich <jim@...>
Date: 2005-05-24T13:47:12+09:00
Subject: Re: Array.=== in Rails Bug

On Monday 23 May 2005 11:55 pm, Markus wrote:
> On Mon, 2005-05-23 at 15:34, Jamis Buck wrote:
> > You can add a ticket to dev.rubyonrails.com. That way it won't get
> > lost in a shuffle of email.
>
> Did that, but in the meantime I found a better solution (and included it
> in the ticket):
>
>         Change AssociationProxy to "class AssociationProxy < Array" and
>         let the C code do its thing.  No muss, no fuss...

FileList in Rake used to inherit from Array to get array-like behavior.  I 
recently changed it to delegate to an internally held array.  I found that 
the delegation allowed a FileList to be used in more places where an Array 
was expected ... mainly because some methods check for the to_ary method to 
see if an object should be treated like an array.

Given the following code:

 [FileList['a', 'b'], FileList['c', 'd']].flatten

Rake 0.5.0 which inherits from Array will return: []
Rake 0.5.3 which delegates to Array will return: ['a', 'b', 'c', 'd']

That's because flatten accesses the array elements directly.  Since FileList 
is lazy loaded, bypassing the methods means that the elements are never 
loaded.  By switching to a delegation method, flatten checks for :to_ary, 
which can be used to trigger loading and make everyone happy.

Short version:  Inheriting from Array is not always the most compatible.

Another moral to the story:  If you want to check for something that is array 
like (but doesn't have to be an array), check to see if it responds to 
to_ary.

-- 
-- Jim Weirich    jim@weirichhouse.org     http://onestepback.org
-----------------------------------------------------------------
"Beware of bugs in the above code; I have only proved it correct, 
not tried it." -- Donald Knuth (in a memo to Peter van Emde Boas)