constants in Perl

When writing Triceps code, I've been whining that it would be great to have symbolic constants in Perl, this would allow to identify the fields of Triceps records by symbolic names that would translate at compile time into integers. Well, it turns out that there are constants in Perl and have been for more than a decade now. They've been there when I've started writing Triceps, just I wasn't aware of them. They're used like this:

use constant X => 1;
use constant Y => 2;

$a[X] = $a[Y] + 1;

They're referenced by names without any prefix, and can be scoped in packages and exported from them like everything else. Duh.