Passing hashes to subroutines

rbi has asked for the wisdom of the Perl Monks concerning the following question:

Hello,
I'm trying to pass different types of variables to a subroutine using named arguments, but I don't understand how it works for hashes. I'm sure I'm missing some basic concept...
I made some trials in the following, but only the first call to dummy works.
Could someone provide me some clue ?
Thank you in advance.

use strict;

my %hash = {a=>'A', b =>'B'};
my @array = [1,2,3];
my $scalar = 'This is a scalar';

dummy(array=>@array, scalar=>$scalar, hash=>{a=>'A', b =>'B'});
dummy(array=>@array, scalar=>$scalar, hash=>%hash);
my $hashref = \%hash;
dummy(array=>@array, scalar=>$scalar, hash=>$hashref);

sub dummy {
   my %args = @_;
   my @a = @{$args{array}};
   my %h = %{$args{hash}};
   my $s = $args{scalar};

   print "scalar is:  $s\n",
      'array is: ', join(',', @a),"\n",
      "hash is:\n", map "$_ => $h{$_}\n", keys %h;
   print "--------\n";
}
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Re: Passing hashes to subroutines by cchampion (Curate) on Jun 08, 2004 at 08:59 UTC
Your declaration for array and hash are wrong. If you use warnings you'll see why. This modified code should do what you want: `#!/usr/bin/perl -w use strict; my %hash = (a=>'A', b =>'B'); # parens, not braces my @array = (1,2,3); # parens, not brakets my $scalar = 'This is a scalar'; # Pass an array REFERENCE dummy(array=>\@array, scalar=>$scalar, hash=>{a=>'A', b =>'B'}); dummy(array=>\@array, scalar=>$scalar, hash=>\%hash); my $hashref = \%hash; dummy(array=>\@array, scalar=>$scalar, hash=>$hashref);` [download] HTH	[reply] [d/l]
Re: Passing hashes to subroutines by blueAdept (Beadle) on Jun 08, 2004 at 14:17 UTC
Hashes must be passed by reference, which means they're nothing more than a single scalar value (in terms of an arguement to a subroutine) If you don't pass its reference, instead just do foo(%hash) then what you're really passing in is an even paired list. HTH. `use strict; use warnings; my %hash1; $hash1{hello} = "world!"; foo(\%hash1); foo( { hello => 'world!!' } ); sub foo { my %hash2 = %{$_[0]}; print "hello " . $hash2{hello} . "\n"; } #output #hello world! #hello world!!` [download]	[reply] [d/l]