perl closures and $_

Question

One of the first things I try to learn in an unfamiliar programming language is how it handles closures. Their semantics are often intertwined with how the language handles scop

Answer 1

Closures only close over lexical variables; $_ is normally a global variable. In 5.10 and above, you can say my $_; to have it be lexical in a given scope (though in 5.18 this was retroactively declared to be experimental and subject to change, so better to use some other variable name).

This produces the output you expected:

use strict;
use warnings;
use 5.010;
my @closures;
foreach my $_ (1..3) {
  # create some closures
  push @closures, sub { say "I will remember $_"; };
}
foreach (@closures) {
  # call the closures to see what they remember
  # the result is not obvious
  &{$_}();
}

Answer 2

$_ is a global variable and should not be used in closure. Before using it assign this to a lexically scoped variable as shown bewlow. This will produce expected o/p.

#!/usr/bin/perl -w

use strict;
my @closures;


foreach (1..3) {
   my $var = $_;
   push @closures, sub { print "I will remember $var"; };
}

foreach (@closures) {
  $_->();
  print "\n";
}