No, I am very much not looking for Scalar::Util::reftype, thought it could indeed replace UNIVERSAL::isa. It still dictates implementation, which is what I'm trying to avoid.

I'm not expecting to rummage around in the internals of an object passed as $args. I'm expecting to deal with something that behaves as a hash. If it's a hash, fine. If it's a tied hash, it ought to work fine too.

Unfortunately, it doesn't:

#!/usr/bin/perl -w

use strict;
use Scalar::Util 'reftype';
use Tie::Hash;

foreach my $package (qw( Scalar Array Code ))
{
    my $h = tie my %new_hash, $package . 'Hash';
    print "Tied $h as a hash based on $package\n";
    print 'It is ' . (UNIVERSAL::isa( $h, 'HASH' ) ? '' : 'not ') . "a
+ HASH\n";
    print 'Its reftype is ' . reftype( $h ) . "\n";
}

package ScalarHash;

sub TIEHASH { bless \(my $foo), $_[0] }

package ArrayHash;

sub TIEHASH { bless [], $_[0] }

package CodeHash;

sub TIEHASH { bless sub {}, $_[0] }
[download]