use strict;
use warnings;

my %h = (1=>2, 3=>4);

sub say { print @_, $/ };

sub get_keys {
    print 'called:';
    if (wantarray()) {
        print 'array:';
    } else {
        print defined wantarray() ? 'scalar' : 'void';
    }
    return keys %h;
}

                             # Output:
say sort get_keys;           # get_keys
say sort get_keys();         # 
say sort &get_keys;          # called:array:13
say sort &get_keys();        # called:array:13
say sort @{[get_keys]};      # called:array:13
say sort @{[get_keys()]};    # called:array:13
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I would have expected that all these outputs would be identical. Here my guesses what went wrong. Could somebody shed some more light on it, please.

• The first case somehow gets interpreted as a bareword - and use strict; doesn't complain because there is a subroutine with that name.
• For the second case I'm really at a loss ...
• The rest of the cases show various ways of making it work. I'm a bit surprised as perlsub says this concerning the calling of functions

             NAME(LIST);    # & is optional with parentheses.
             NAME LIST;     # Parentheses optional if predeclared/import
  +ed.
             &NAME(LIST);   # Circumvent prototypes.
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  Therefore there shouldn't be any difference between get_keys() and &get_keys() as get_keys doesn't use prototypes.

In case it matters: This is perl, v5.6.1 built for i386-linux.

And btw, I came across this when I tested App::Ack (Version 1.50) and tried to run ack --help types which doesn't display any types for me. Tracking it down, I reached the following line in App::Ack::show_help_types, which exhibits the behaviour of case 2 above.

for my $type ( sort( filetypes_supported() ) ) {
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