Closures

In Perl or PHP 5.3+, closures are implemented as anonymous subroutines with lasting references to lexical variables outside their own scopes.
Perl example:

#!/usr/bin/perl

sub test_it {
    my ($count) = @_;
    return sub { ++$count; };
}

my $test1 = test_it(10);
my $test2 = test_it(50);
print $test1->(), "\n";         # 11
print $test2->(), "\n";         # 51
print $test1->(), "\n";         # 12
print $test2->(), "\n";         # 52

PHP distinguishes between read-only closures or read-write closures:

#!/usr/bin/php

<?php
function test_it_ro($count) {
    return function() use($count) {
        return ++$count;
    };
}
function test_it_rw($count) {
    return function() use(&$count) {
        return ++$count;
    };
}
$test1 = test_it_ro(10);
$test2 = test_it_ro(50);
print $test1()."\n";            // 11
print $test2()."\n";            // 51
print $test1()."\n";            // 11
print $test2()."\n";            // 51

$test1 = test_it_rw(10);
$test2 = test_it_rw(50);
print $test1()."\n";            // 11
print $test2()."\n";            // 51
print $test1()."\n";            // 12
print $test2()."\n";            // 52
?>