Question

In Perl before 5.10 there is no “state” declaration.

I’ve come across an example of creating static variables in these Perls: my $x if 0. The if 0 conditional makes the variable act like a static variable:

use strict; use warnings;
add() for 1..7;

sub add {
    my @arr = () if 0;

    push @arr, '+';
    print @arr, "\n";
}

prints:

+
++
+++
++++
+++++
++++++
+++++++

Is this behaviour consistent in all versions of Perl before 5.10?

Answer 1

I’ve always used scoping braces to create static variables.

add() for 1..2;       # Append to existing.
add('foo', 'bar');    # Re-initialize if args are passed.
add() for 1..2;       # Append to existing.
{
    my @arr;
    sub add {
        @arr = @_ if @_;
        push @arr, '+';
        print @arr, "\n";
    }
}