I defined hash and array constants, When passing those to a function, I'll have to pass them as references. However I'm wondering what the correct syntax is.

Consider this example:

#!/usr/bin/perl
use strict;
use warnings;

use constant AC => qw(a b c);

sub f($)
{
    print "ref=", ref $_[0], "\n";
    print "$_\n" foreach (@$_[0]);
}

f(\AC);

When I run it I get:

ref=SCALAR
Use of uninitialized value $_ in concatenation (.) or string at /run/media/whatever/constref.pl line 10.

The Perl debugger prints C as an array:

13: f(\AC);
  DB<1> x AC
0  'a'
1  'b'
2  'c'
  DB<2> c

CodePudding user response：

AC is a reference to an array, not an array. Simply replace

f(\AC);

with

f(AC);

Note that the referenced array isn't constant, just the reference. Use Readonly to create an array that can't be modified.

CodePudding user response：

The only array in your code is @_ the array used to pass parameters into your subroutine. Your constant is a list, not an array. And you can't take a reference of a list.

I can think of three options for you.

1. Don't pass a reference, just pass the constant. You need to lose the prototype on the subroutine (but I'm not sure what it's gaining you anyway):

   use constant AC => qw(a b c);
   
   sub f
   {
       print "ref=", ref $_[0], "\n";
       print "$_\n" foreach (@_);
   }
   
   f(AC);
   

2. Make use of the fact that constants are actually subroutines and pass a reference to a subroutine instead:

   use constant AC => qw(a b c);
   
   sub f($)
   {
       print "ref=", ref $_[0], "\n";
       print "$_\n" foreach ($_[0]->());
   }
   
   f(\&AC);
   

3. Switch to using a better constants library (like Readonly) instead.