Perl constant array

Question

use constant {
    COLUMNS => qw/ TEST1 TEST2 TEST3 /,
}

Can I store an array using the constant package in Perl?

Whenever I go on to try to use the array like my @attr = (COLUMNS);, it does not contain the values.

Even after modifying your code as shown by the answers below, the result will not be very useful as you can still modify the contents of a constant reference: perl -e 'use constant C => [1,2,3]; C->[1] = 5; print C->[1]. "\n";' — josch
– josch, Commented Sep 5, 2018 at 8:25

Himanshu · Accepted Answer · 2013-08-13 05:58:16Z

12

Or remove the curly braces as the docs show :-

  1 use strict;
  2 use constant COLUMNS => qw/ TEST1 TEST2 TEST3 /;
  3 
  4 my @attr = (COLUMNS);
  5 print @attr;

which gives :-

 % perl test.pl
TEST1TEST2TEST3

Your code actually defines two constants COLUMNS and TEST2 :-

use strict;
use constant { COLUMNS => qw/ TEST1 TEST2 TEST3 /, };

my @attr = (COLUMNS);
print @attr;
print TEST2

and gives :-

% perl test.pl
TEST1TEST3

answered Aug 12, 2013 at 13:45

Himanshu

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1 Comment

+1 The use of braces (a hashref) imposes an interpretation the OP doesn't want.

Deanna · Accepted Answer · 2020-10-14 15:24:05Z

9

Use a + to signify that it's a contant.

use constant {
  COLUMNS => [qw/ TEST1 TEST2 TEST3 /],
};

print @{+COLUMNS};

The + is a hint to the interpreter that the constant is actually a constant, and not a bare word. See this reply for more details.

Deanna

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answered Aug 12, 2013 at 13:37

mpapec

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It is a hint to interpreter, to make disambiguation. Check stackoverflow.com/a/21173602/223226