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Postings from August 2003
Dave Mitchell <davem@fdgroup.com> writes:
>On Tue, Aug 19, 2003 at 11:31:48PM -0400, Kurt Starsinic wrote:
>> I suggest that it's a closure when the language supports
>> associating bindings to the subroutine. In Perl, this is always
>> and only the case for anonymous subroutines, whether or not the
>> number of private bindings > 0.
>>
>> So it seems to me that, in Perl, a named subroutine is never a
>> closure, and an anonymous subroutine is always a closure.
>
>But named subs also capture their lexical state at creation time,
Things get confusing:
sub harry
{
my $foo = shift;
sub fred { print "$foo\n" }
}
harry('Ouch');
harry('Weird');
fred();
>so I would call them closures too:
>
>X.pm:
> package X;
> sub new { my $x = $_[1]; bless \$x }
> sub DESTROY { print "${$_[0]} destroyed\n" }
>
> my $x1 = X->new('x1');
> my $x2 = X->new('x2');
> sub f { $x2 }
>p:
> #!/usr/bin/perl -w
>
> print "in main\n";
> use lib '.';
> use X;
>
>gizmo [d]$ ./p
>x1 destroyed
>in main
>x2 destroyed
>gizmo [d]$
>
>Here, f captures $x2 and so stops it being destroyed at the end of
>the compilation of X.pm. That is an important behaviour that deserves
>a label. 'Closure' seems as good a label as any to me.
>
>Similar comments aply to, eg
>
> {
> my $c = 0;
> sub inc { $c++ }
> sub dec { $c-- }
> }
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