Larry Wall wrote:
On Mon, Nov 18, 2002 at 08:05:47AM +1100, Damian Conway wrote:
: I still think my original:
:
: sub bar(; $foo = $topic) is given($topic) {...}
:
: is the appropriate compromise.
Won't fly. Referring to something lexical before it's declared is
a no-no.
I would maintain that that depends on the associativity of C<is given>. ;-)
But you mean in a strict left-to-right parsing sense.
I think we need some other way of indicating the outer topic
if we're gonna use it as a default, and I think we do want that.
I think so too.
Perhaps it's a good time for a real keyword for use in defaults:
sub bar(; $foo = topic) {...}
That would have to be:
sub bar(; $foo = topic) is given($whatever) {...}
wouldn't it? Otherwise the topic is C<undef>.
Anyway, I think a C<topic> keyword is NQR.
For a start, it introduces a (rather too) subtle difference between:
sub bar($foo = topic) is given($whatever) {...}
and:
sub bar($foo is topic) is given($whatever) {...}
not to mention the pain in continually needing to explain why this is okay:
sub bar($foo is topic = topic) is given($whatever) {...}
but this is not:
sub bar($foo = topic is topic) is given($whatever) {...}
Hmmmmm. Given that the topic is in some sense a property of the lexical
scope of the subroutine body, this might be a possibility:
sub bar($foo is MY.topic) is given($whatever) {...}
But I think there's a better solution. See below.
That would let us work it nicely for arrays too:
sub bar(*@args = [topic]) {...}
Without the [], people might get confused about what to do with a $_
containing an array reference. But maybe that means it should really
be a magical variable
Yep.
so we can distinguish
sub bar(*@args = $<mumble>) {...} # default to [$_]
sub bar(*@args = @$<mumble>) {...} # default to @$_
What <mumble> might be is an interesting, er, topic.
I would argue it ought to be just $_, which is, after all,
the One True Topic. And conveniently lexically predeclared in all scopes.
I would also argue that it ought not be called anything else.
Surely don't want two specially named variables for the topic?
Damian
