Re: StringIO is not IO?

On 12/10/2007, Eric Mahurin <[e-mail]> wrote:
> On 10/12/07, Hongli Lai <[e-mail]> wrote:
> > 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.
>
> I suggest that you either use another way to figure out how you should
> treat an argument (like number of arguments or a flag) or don't use
> "multi-methods" (split the single method into multiple so that you
> don't have to look at the "type" to determine what to do).
> Multi-methods really aren't a good thing in ruby and clash with the
> concept of duck-typing.
>

I also hit this particular case. The question "Is it an IO or a
filename?" can be solved by detecting the read/write method that would
be used to get/store the data. If it's not there you can try and use
the object as filename.
But in general writing methods that do different things depending on
the kind of data they receive is quite hard in ruby.

Thanks

Michal