# $File: //member/autrijus/Class-PseudoHash/PseudoHash.pm $ $Author: autrijus $
# $Revision: #1 $ $Change: 1 $ $DateTime: 2002/06/11 08:35:12 $

package Class::PseudoHash;
use 5.005;

$Class::PseudoHash::VERSION = '1.01';

use strict;
use vars qw/$FixedKeys $Obj $Proxy/;
use constant NO_SUCH_FIELD => 'No such pseudohash field "%s"';
use constant NO_SUCH_INDEX => 'Bad index while coercing array into hash';
use overload (
    '%{}'  => sub { $$Obj = $_[0]; return $Proxy },
    '""'   => sub { overload::AddrRef($_[0]) },
    '0+'   => sub { 
	my $str = overload::AddrRef($_[0]);
	hex(substr($str, index($str, '(') + 1, -1));
    },
    'bool' => sub { 1 },
    'cmp'  => sub { "$_[0]" cmp "$_[1]" },
    '<=>'  => sub { "$_[0]" cmp "$_[1]" }, # for completeness' sake
    'fallback' => 1,
);

=head1 NAME

Class::PseudoHash - Emulates Pseudo-Hash behaviour via overload

=head1 VERSION

This document describes version 1.01 of Class::PseudoHash, released
June 20, 2002

=head1 SYNOPSIS

    use Class::PseudoHash;

    my @args = ([qw/key1 key2 key3 key4/], [1 .. 10]);
    my $ref1 = fields::phash(@args);		# phash() override
    my $ref2 = Class::PseudoHash->new(@args);	# constructor syntax

=head1 DESCRIPTION

Due to its impact on overall performance of ordinary hashes, pseudo-hashes
are deprecated in perl v5.8, and will cease to exist in perl v5.10.  By then,
the C<fields> pragma is supposed to change to use a different implementation.

Although L<perlref/Pseudo-hashes: Using an array as a hash> recommends
against depending on the underlying implementation (i.e. using the first
array element as hash indice), there are undoubtly many brave souls still
writing such code, and fearing that the elimination of pseudo-hashes will
require a massive rewrite of their programs.

As one of the primary victims, I tried to devise a drop-in solution that 
could emulate exactly the same semantic of pseudo-hashes, thus keeping 
all my legacy code intact.  So C<Class::PseudoHash> was born.

Hence, if your code use the preferred C<fields::phash()> function, just write:

    use fields;
    use Class::PseudoHash;

then everything will work like before.  If you are creating pseudo-hashes 
by hand (C<[{}]> anyone?), just write this:

    $ref = Class::PseudoHash->new;

and use the returned object in whatever way you like.

=head1 NOTES

If you set C<$Class::PseudoHash::FixedKeys> to a false value and tries
to access a non-existent hash key, then a new pseudo-hash entry will be
created silently.  This is most useful if you're already using untyped
pseudo-hashes, and don't want the compile-time checking feature.

Compile-time validating of keys is not possible with this module, for
obvious reasons.  Also, the performance will not be as fast as typed
pseudo-hashes (but generally faster than untyped ones).

=cut

$FixedKeys = 1;

sub import {
    no strict 'refs';

    my $class = shift;
    tie %{$Proxy}, $class;

    *{'fields::phash'} = sub {
	$class->new(@_);
    } unless defined $_[0];
}

sub new {
    my $class = shift;
    my @array = undef;

    if (UNIVERSAL::isa($_[0], 'ARRAY')) {
	foreach my $k (@{$_[0]}) {
	    $array[$array[0]{$k} = @array] = $_[1][$#array];
	}
    }
    else {
	while (my ($k, $v) = splice(@_, 0, 2)) {
	    $array[$array[0]{$k} = @array] = $v;
	}
    }

    bless(\@array, $class);
}

sub FETCH {
    my ($self, $key) = @_;

    $self = $$$self;

    return $self->[
	$self->[0]{$key} >= 1
	    ? $self->[0]{$key} :
	defined($self->[0]{$key})
	    ? _croak(NO_SUCH_INDEX) :
	$FixedKeys
	    ? _croak(NO_SUCH_FIELD, $key) :
	@$self
    ];
}

sub STORE {
    my ($self, $key, $value) = @_;

    $self = $$$self;

    return $self->[
	$self->[0]{$key} >= 1
	    ? $self->[0]{$key} :
	defined($self->[0]{$key})
	    ? _croak(NO_SUCH_INDEX) :
	$FixedKeys
	    ? _croak(NO_SUCH_FIELD, $key) :
	@$self
    ] = $value;
}

sub _croak {
    require Carp;
    Carp::croak(sprintf(shift, @_));
}

sub TIEHASH {
    bless \$Obj => shift;
}

sub FIRSTKEY {
    scalar keys %{$${$_[0]}->[0]};
    each %{$${$_[0]}->[0]};
}

sub NEXTKEY {
    each %{$${$_[0]}->[0]};
}

sub EXISTS {
    exists $${$_[0]}->[0]{$_[1]};
}

sub DELETE {
    delete $${$_[0]}->[0]{$_[1]};
}

sub CLEAR {
    @{$${$_[0]}} = ();
}

1;

=head1 SEE ALSO

L<fields>,
L<perlref/Pseudo-hashes: Using an array as a hash>

=head1 AUTHORS

Autrijus Tang E<lt>autrijus@autrijus.orgE<gt>

=head1 COPYRIGHT

Copyright 2001, 2002 by Autrijus Tang E<lt>autrijus@autrijus.orgE<gt>.

This program is free software; you can redistribute it and/or 
modify it under the same terms as Perl itself.

See L<http://www.perl.com/perl/misc/Artistic.html>

=cut