An anonymous subroutine that grabs lexical variables from its containing environment is a closure. Remember that it does not just take a snapshot of the value at the instant the anonymous subroutine is seen.
# declare an anonymous subroutine, and return a reference to it.
my $foo = 10;
$rs = sub {
print "Foo is $foo\n"; # Grabs $foo
};
&$rs(); # Call the closure through the reference
The closure keeps the grabbed variable's value around even when the variable goes out of scope.
sub init_counter {
my $num = shift; # lexical variable to be grabbed
$rs = sub { print $num++," "; };
return $rs;
}
$rs_counter = init_counter(10); # $rs_counter is a ref-to-sub
for (1..5) {&$rs_counter()}; # Prints 10 through 14