From: Austin Ziegler <austin@...>
Date: 2002-07-10T02:18:11+09:00
Subject: Re: for ... else ... end

On Wed, 10 Jul 2002 01:52:38 +0900, David Alan Black wrote:
> I still don't see how a code block can have an 'else' clause.
> Wouldn't this make for some awfully bizarre code?

I can't, either -- which is why I'm asking the questions:

1. How would this work in a case where there is no loop, but just a
   block?
2. How would I construct my own each member function to take
   advantage of the else (and possibly other clauses)?

I can see the utility of the construct, but I think it makes a lot
more sense in languages where there are real control structures.

> array.each {|e| else puts "Empty array"}

> Given an empty array, this else clause would execute. [...] And,
> come to think of it.... shouldn't the block not be entered at all
> if the array is empty? What the "else" thing means is that the
> block *will* be entered. I wish I knew the technical term for why
> that isn't OK :-) but doesn't it feel very non-OK?

Agreed. I'd prefer to do that as:

puts "Empty array" if array.empty?
array.each { |e| puts e } unless array.empty?

It might be nice to have some syntactic sugar that does something
like that:

array.each { |e| puts e } unless array.empty then puts "Empty array"

(Not currently possible, AFAIK, and probably really nasty in the
interpretation of same.)

Why not something like:

case array.each { |e| puts e }
    when array.empty?
        puts "Empty array"
    when broken # The ugly part
        puts "Broke from each early"
    else
        puts "Done processing"
end

I don't know if that will work (except, of course, 'broken', which
won't work), but it seems to be conceptually cleaner. IMO.

> It seems to me to be crossing all sorts of borders and boundaries
> for a proc/block to have this kind of knowledge. Is a block of
> code really supposed to know whether or not it was executed,
> without any explicit test?

I think that it's a bad idea, myself.

> I guess this thread is bringing out my Ruby-conservative streak :-)
> I'm personally very happy to do something like this (which I know
> isn't identical to your example, but still):

FWIW, this was someone else's example that I adapted from a
for...end format to an each do...end format -- because I don't think
that it's necessarily a good way of doing it.

-austin
-- Austin Ziegler, austin@halostatue.ca on 2002.07.09 at 13.06.12