In a message dated 2 Sep 2002, Aaron Sherman writes:
> I'm working on a library of rules and subroutines for dealing with UNIX
> system files. This is really just a mental exercise to help me grasp the
> new pattern stuff from A5.
>
> I've hit a snag, though, on hypothetical variables. How would this code
> work?
>
> {
> my $x = 2;
> my $y = "The grass is green";
> $y =~ /(gr\w+) {let $x = $1}/;
> }
>
> I assume that it would change C<$x> from C<2> to C<"grass">.
Yes. $0{x} would be set to "grass". A lexical variable has been defined
in the same scope as the hypothetical with the same name, so its value is
set hypothetically (is hypothetically bound to?) $0{x}. When the rule
succeeds, $x's hypothetical value is made permanent.
> But here's
> the case where I'm concerned:
>
> module foo;
> rule gr_word { (gr\w+) {let $x = $1} }
> ----my code----
> use foo;
> my $x = 2;
> "The grass is green" =~ /<gr_word>/;
>
> Would my local C<$x> be reset to C<"grass">?
No. $0{x} would be set to "grass". $x would stay as 2. $x is in a
different scope from the hypothetical, so it doesn't get touched.
> That would seem to lead to
> some very ugly namespace problems, since the module user never asked to
> have C<$x> replaced, it's just a silent side-effect.
Nope, shouldn't have any effect.
> Please tell me there's some magic way that this works, so that I'm wrong
> :)
I don't think it's magic. It's just scoping.
Trey
