From: Hongli Lai <h.lai@...>
Date: 2007-10-13T03:37:36+09:00
Subject: Re: StringIO is not IO?

Eric Mahurin wrote:
> Since StringIO doesn't use IO to base its implementation, it is not an IO.
> 
> Why does it matter?  If you use standard duck typing, it shouldn't.
> Class hierarchy doesn't matter with duck typing.  Classes are just an
> implementation detail with duck typing.  You are best off not looking
> #is_a?, #respond_to?, etc.  Just assume the object can do the methods
> you'll be using and use.

Well, some of my code can write its output to a file (specified by a 
filename string) or to an IO object. So my code first checks whether 
output.is_a?(IO), which is not the case.

RMagick seems to do the same thing. I tried making RMagick write its 
output to a StringIO, but that failed because it thought it isn't an IO 
object. I spent quite some time on debugging these two problems, and I 
guess that am not the first one.

Finally, when one thinks about it logically, StringIO *should* be an IO. 
There's even the word 'IO' in its class name. So why not do an 'include 
IO' in StringIO? That would solve a lot of problems and make the class 
hierarchy more logical.