From: George Ogata <g_ogata@...>
Date: 2004-06-06T04:23:38+09:00
Subject: Re: How to ducktype a Hash?

"Sean O'Dell" <sean@celsoft.com> writes:

> The problem isn't that the object doesn't respond to the methods I
> need, it's that it DOES respond to the methods I need, but the
> methods don't do what I expect them to do.  In this case,
> duck-typing simply doesn't work for me.  I found this error through
> duck-typing, but it existed for weeks before I realized that some
> objects were quietly trashing sections of data I was passing around,
> because strings, arrays and others all respond to [] and []=, but
> DON'T contain objects quite the same way hashes do.

I thought the idea was that if you unit test each piece as you write
it, these sorts of things are usually caught in time.

> I just don't like this duck-typing business.  I can handle dynamic
> typing, but I wish there were something more solid about the typing,
> at least a way to know when an object implements a certain interface
> or not, so I can tell an array-like object from a hash-like object.

As others have suggested, you don't HAVE to use duck-typing, but if
you choose that path, you need to provide your own type checks, and
shove all your classes in the right place in the right heirarchies.
However, anecdotal evidence (my own and by what others have said here
before) suggests to me that usually type checks have been weened from
in favor of a good unit test.  Hence, I imagine, the lack of
strict-typing facilities in the language.