FM / Tie

/usr/share/perl5/Tie

Name	Size	Mode	Actions
Array.pm	7318	0644	edit dl rm
File.pm	77444	0644	edit dl rm
Handle.pm	4202	0644	edit dl rm
Hash.pm	7639	0644	edit dl rm
Memoize.pm	4251	0644	edit dl rm
RefHash.pm	6237	0644	edit dl rm
Scalar.pm	4164	0644	edit dl rm
StdHandle.pm	1398	0644	edit dl rm
SubstrHash.pm	5404	0644	edit dl rm

Edit: /usr/share/perl5/Tie/Hash.pm (7639B)

package Tie::Hash;

our $VERSION = '1.05';

=head1 NAME

Tie::Hash, Tie::StdHash, Tie::ExtraHash - base class definitions for tied hashes

=head1 SYNOPSIS

package NewHash;
    require Tie::Hash;

@ISA = qw(Tie::Hash);

sub DELETE { ... }		# Provides needed method
    sub CLEAR { ... }		# Overrides inherited method

package NewStdHash;
    require Tie::Hash;

@ISA = qw(Tie::StdHash);

# All methods provided by default, define
    # only those needing overrides
    # Accessors access the storage in %{$_[0]};
    # TIEHASH should return a reference to the actual storage
    sub DELETE { ... }

package NewExtraHash;
    require Tie::Hash;

@ISA = qw(Tie::ExtraHash);

# All methods provided by default, define 
    # only those needing overrides
    # Accessors access the storage in %{$_[0][0]};
    # TIEHASH should return an array reference with the first element
    # being the reference to the actual storage 
    sub DELETE { 
      $_[0][1]->('del', $_[0][0], $_[1]); # Call the report writer
      delete $_[0][0]->{$_[1]};		  #  $_[0]->SUPER::DELETE($_[1])
    }

package main;

tie %new_hash, 'NewHash';
    tie %new_std_hash, 'NewStdHash';
    tie %new_extra_hash, 'NewExtraHash',
	sub {warn "Doing \U$_[1]\E of $_[2].\n"};

=head1 DESCRIPTION

This module provides some skeletal methods for hash-tying classes. See
L<perltie> for a list of the functions required in order to tie a hash
to a package. The basic B<Tie::Hash> package provides a C<new> method, as well
as methods C<TIEHASH>, C<EXISTS> and C<CLEAR>. The B<Tie::StdHash> and
B<Tie::ExtraHash> packages
provide most methods for hashes described in L<perltie> (the exceptions
are C<UNTIE> and C<DESTROY>).  They cause tied hashes to behave exactly like standard hashes,
and allow for selective overwriting of methods.  B<Tie::Hash> grandfathers the
C<new> method: it is used if C<TIEHASH> is not defined
in the case a class forgets to include a C<TIEHASH> method.

For developers wishing to write their own tied hashes, the required methods
are briefly defined below. See the L<perltie> section for more detailed
descriptive, as well as example code:

=over 4

=item TIEHASH classname, LIST

The method invoked by the command C<tie %hash, classname>. Associates a new
hash instance with the specified class. C<LIST> would represent additional
arguments (along the lines of L<AnyDBM_File> and compatriots) needed to
complete the association.

=item STORE this, key, value

Store datum I<value> into I<key> for the tied hash I<this>.

=item FETCH this, key

Retrieve the datum in I<key> for the tied hash I<this>.

=item FIRSTKEY this

Return the first key in the hash.

=item NEXTKEY this, lastkey

Return the next key in the hash.

=item EXISTS this, key

Verify that I<key> exists with the tied hash I<this>.

The B<Tie::Hash> implementation is a stub that simply croaks.

=item DELETE this, key

Delete the key I<key> from the tied hash I<this>.

=item CLEAR this

Clear all values from the tied hash I<this>.

=item SCALAR this

Returns what evaluating the hash in scalar context yields.

B<Tie::Hash> does not implement this method (but B<Tie::StdHash>
and B<Tie::ExtraHash> do).

=back

=head1 Inheriting from B<Tie::StdHash>

The accessor methods assume that the actual storage for the data in the tied
hash is in the hash referenced by C<tied(%tiedhash)>.  Thus overwritten
C<TIEHASH> method should return a hash reference, and the remaining methods
should operate on the hash referenced by the first argument:

package ReportHash;
  our @ISA = 'Tie::StdHash';

sub TIEHASH  {
    my $storage = bless {}, shift;
    warn "New ReportHash created, stored in $storage.\n";
    $storage
  }
  sub STORE    {
    warn "Storing data with key $_[1] at $_[0].\n";
    $_[0]{$_[1]} = $_[2]
  }

=head1 Inheriting from B<Tie::ExtraHash>

The accessor methods assume that the actual storage for the data in the tied
hash is in the hash referenced by C<(tied(%tiedhash))-E<gt>[0]>.  Thus overwritten
C<TIEHASH> method should return an array reference with the first
element being a hash reference, and the remaining methods should operate on the
hash C<< %{ $_[0]->[0] } >>:

package ReportHash;
  our @ISA = 'Tie::ExtraHash';

sub TIEHASH  {
    my $class = shift;
    my $storage = bless [{}, @_], $class;
    warn "New ReportHash created, stored in $storage.\n";
    $storage;
  }
  sub STORE    {
    warn "Storing data with key $_[1] at $_[0].\n";
    $_[0][0]{$_[1]} = $_[2]
  }

The default C<TIEHASH> method stores "extra" arguments to tie() starting
from offset 1 in the array referenced by C<tied(%tiedhash)>; this is the
same storage algorithm as in TIEHASH subroutine above.  Hence, a typical
package inheriting from B<Tie::ExtraHash> does not need to overwrite this
method.

=head1 C<SCALAR>, C<UNTIE> and C<DESTROY>

The methods C<UNTIE> and C<DESTROY> are not defined in B<Tie::Hash>,
B<Tie::StdHash>, or B<Tie::ExtraHash>.  Tied hashes do not require
presence of these methods, but if defined, the methods will be called in
proper time, see L<perltie>.

C<SCALAR> is only defined in B<Tie::StdHash> and B<Tie::ExtraHash>.

If needed, these methods should be defined by the package inheriting from
B<Tie::Hash>, B<Tie::StdHash>, or B<Tie::ExtraHash>. See L<perltie/"SCALAR">
to find out what happens when C<SCALAR> does not exist.

=head1 MORE INFORMATION

The packages relating to various DBM-related implementations (F<DB_File>,
F<NDBM_File>, etc.) show examples of general tied hashes, as does the
L<Config> module. While these do not utilize B<Tie::Hash>, they serve as
good working examples.

=cut

use Carp;
use warnings::register;

sub new {
    my $pkg = shift;
    $pkg->TIEHASH(@_);
}

# Grandfather "new"

sub TIEHASH {
    my $pkg = shift;
    my $pkg_new = $pkg -> can ('new');

if ($pkg_new and $pkg ne __PACKAGE__) {
        my $my_new = __PACKAGE__ -> can ('new');
        if ($pkg_new == $my_new) {  
            #
            # Prevent recursion
            #
            croak "$pkg must define either a TIEHASH() or a new() method";
        }

warnings::warnif ("WARNING: calling ${pkg}->new since " .
                          "${pkg}->TIEHASH is missing");
	$pkg -> new (@_);
    }
    else {
	croak "$pkg doesn't define a TIEHASH method";
    }
}

sub EXISTS {
    my $pkg = ref $_[0];
    croak "$pkg doesn't define an EXISTS method";
}

sub CLEAR {
    my $self = shift;
    my $key = $self->FIRSTKEY(@_);
    my @keys;

while (defined $key) {
	push @keys, $key;
	$key = $self->NEXTKEY(@_, $key);
    }
    foreach $key (@keys) {
	$self->DELETE(@_, $key);
    }
}

# The Tie::StdHash package implements standard perl hash behaviour.
# It exists to act as a base class for classes which only wish to
# alter some parts of their behaviour.

package Tie::StdHash;
# @ISA = qw(Tie::Hash);		# would inherit new() only

sub TIEHASH  { bless {}, $_[0] }
sub STORE    { $_[0]->{$_[1]} = $_[2] }
sub FETCH    { $_[0]->{$_[1]} }
sub FIRSTKEY { my $a = scalar keys %{$_[0]}; each %{$_[0]} }
sub NEXTKEY  { each %{$_[0]} }
sub EXISTS   { exists $_[0]->{$_[1]} }
sub DELETE   { delete $_[0]->{$_[1]} }
sub CLEAR    { %{$_[0]} = () }
sub SCALAR   { scalar %{$_[0]} }

package Tie::ExtraHash;

sub TIEHASH  { my $p = shift; bless [{}, @_], $p }
sub STORE    { $_[0][0]{$_[1]} = $_[2] }
sub FETCH    { $_[0][0]{$_[1]} }
sub FIRSTKEY { my $a = scalar keys %{$_[0][0]}; each %{$_[0][0]} }
sub NEXTKEY  { each %{$_[0][0]} }
sub EXISTS   { exists $_[0][0]->{$_[1]} }
sub DELETE   { delete $_[0][0]->{$_[1]} }
sub CLEAR    { %{$_[0][0]} = () }
sub SCALAR   { scalar %{$_[0][0]} }

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