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Postings from August 2003
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,
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-- }
}
--
Never do today what you can put off till tomorrow.
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