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perl

How to pass a hash and a scalar to a Perl subroutine?

I'm doing this:

foo(('x' => 'y'), 'bar');

use strict;

sub foo {
  my ($hash, $s) = @_;
  my %e = %$hash;
  print %e{'x'};
  print $s;
}

I'm getting:

Can't use string ("x") as a HASH ref while "strict refs" in use at a.pl line 7.

What is the right way to pass a hash and a scalar to a subroutine?

Solution

  • ('x' => 'y') isn't a "hash", it's a list with two elements, and the parentheses don't even matter. What you're calling is the same as foo('x', 'y', 'bar').

    If you want to pass a hashref as the first argument, you can use the anonymous hash reference constructor: foo({ x => 'y' }, 'bar').

    Side note: print %e{'x'} should be print $e{'x'}. Or more simply, you can use the ->{} operator to dereference and access at the same time: print $hash->{'x'}.