At 03:03 PM 8/5/00 -0400, Mark-Jason Dominus wrote:
>3. Variables should be lexical by default:
>
> a. Perl should be conservative about inference and issue a warning
> when scopes appear to overlap, as in the example above. In such
> cases a declaration at the outer scope may be required for
> correct behavior.
>
> b. Perl should be more liberal about inference and should try to do
> the right thing without warnings, as in the example above.
>
> This is my position (although I haven't committed to 3a or 3b yet
> because the details are not explicit), and it's *also* consistent
> with what you say above, so I'm not sure that you're even
> disagreeing with me.
>[snip]
>Example 3:
>
> YOU WRITE: PERL INFERS THAT YOU MEANT:
>
> my $switch;
> if (condition) { if (condition) {
> $switch = 1; my $switch = 1;
> } }
> # ... # ...
> print "..." if $switch; print "..." if $switch;
>
> WARNING: $switch on line 2 is not
> the same as $switch on line 5
>
>
>Here's the one with the problem. Perl infers too many declarations
>and you don't get what you want. But you do get a warning. To fix
>it, you add the declaration to make it look like example 1. This is
>not obfuscated or confusing because the resulting code has exactly the
>same meaning in Perl 5 and in Perl 6.
>
>The rule for how Perl infers 'my' is: Perl infers a 'my' at the
>innermost possible scope for every variable that isn't explicitly
>declared in some outer scope.
What says that Perl must infer the declaration of the outer $switch before
the inner block, rather than right before its first use:
if (condition) {
my $switch = 1;
}
# ...
my $switch;
print "..." if $switch;
Don't get me wrong, I agree with the way you had it (inferred declarations
occur as early as possible in the inferred scope). But it seems that it
could be either way and I would like to know whether there is any advantage
to doing it the other way.
Doing it the other way would appear to make the warning impossible, which
is certainly a disadvantage.
--
Peter Scott
Pacific Systems Design Technologies
