From: Hal Fulton <hal9000@...>
Date: 2003-12-15T08:39:06+09:00
Subject: Re: All there is to know about Duck Typing (was: inplace assignment)

John Carter wrote:
> You could invoke any method on any object of any class.
> 
> But what would happen thereafter depended very much on the class of
> the instance.
> 
> The default behaviour was system settable, either
>   * print a debug statement to the log file, or
>   * Do nothing and just return.
> 
> 
> For example, the Person object wouldn't have a
> "paint_yourself(colour)" method. Thus if you had a mixed bag of
> objects, you could tell the whole bag to "paint_yourself( blue)", the
> drawable objects would paint themselves blue and the people would just
> do nothing.
> 
> In practice mixed bags of objects were not all that common though, but
> if duck typing is more accessible they may start to be.
> 
> It's sort of like the default parameter on Hash.new what do you want
> hash[unknown_key] to be today? What do you want
> object.unknown_method() to do today?

Hmm. I'm uncertain how good this idea is in general practice.

But unless I'm missing something, it would be trivial to do this
in Ruby, simply by defining method_missing for every class.

Hal