From: Massimiliano Mirra <list@...>
Date: 2002-09-29T21:33:07+09:00
Subject: Re: thoughts on typelessness

On Sun, Sep 29, 2002 at 12:09:32PM +0900, dblack@candle.superlink.net wrote:
> Another thing people often point to that might deter people from
> learning a truly type-unchecked programming style is the wordiness of
> the most often-mentioned alternative, the "respond_to?" test:
> 
>    thing.action if thing.respond_to?(action)

Do you really want your method to go on even if `thing' doesn't
respond to `action'?  Similarly, would you do the following?

    thing.action if thing.is_a?(Thing)

That would look as redundant (and dangerous).

> This has the look and feel of duplicate, workaround code.  Whereas
> this:
> 
>    raise ArgumentError unless obj.is_a?(Thing)

Sorry David, I feel you're comparing apples and oranges here. :-)

I don't think `thing.action if thing.respond_to?(action)' is a likely
case.  The following would:

    raise ArgumentError unless thing.respond_to?(action)
    thing.action

Which as you can see is just symmetric to:

    raise ArgumentError unless obj.is_a?(Thing)
    thing.action

> the #respond_to? test itself is by no means the most concise or
> elegant available idiom.

If verbs were always chosen for method names, this could be nice:

    obj.can?(:mkdir)

And this wouldn't be too bad:

    def meth(obj)
      continue if
        obj.can?(:mkdir) and
	obj.can?(:recurse) and
	obj.can?(:list)
	

Or more concise:

    def meth(obj)
      continue if obj.can?(:mkdir, :recurse, :list)



Massimiliano (bard on IRC)