Question

I’ve been using the [constant] pragma, and have a quick question on how I can declare a constant list:

use constant {
   LIST_ONE   => qw(this that the other),    #BAD
   LIST_TWO   => ("that", "this", "these", "some of them"),   #BAR
   LIST_THREE => ["these", "those", "and thems"],   #WORKS
};

The problem with the last one is that it creates a reference to a list:

use constant {
   LIST_THREE => ["these", "those", "and thems"],
};

# Way 1: A bit wordy and confusing

my $arrayRef = LIST_THREE;
my @array = @{$arrayRef};

foreach my $item (@array) {
   say qq(Item = "$item");
}

# Way 2: Just plain ugly
foreach my $item (@{&LIST_THREE}) {

   say qq(Item = "$item");
}

This works, but it’s on the ugly side.

Is there a better way of creating a constant list?

I realize that constants are really just a cheap way of creating a subroutine which returns the value of the constant. But, subroutines can also return a list too.

What is the best way to declare a constant list?

Answer 1

According to the documentation, if you do:

use constant DAYS => qw( Sunday Monday Tuesday Wednesday Thursday Friday Saturday);

…you can then do:

my @workdays = (DAYS)[1..5];

I’d say that’s nicer than the two ways of referencing constant lists that you have described.