package Tie::Hash;
+our $VERSION = '1.03';
+
=head1 NAME
-Tie::Hash, Tie::StdHash - base class definitions for tied hashes
+Tie::Hash, Tie::StdHash, Tie::ExtraHash - base class definitions for tied hashes
=head1 SYNOPSIS
package NewHash;
require Tie::Hash;
-
- @ISA = (Tie::Hash);
-
+
+ @ISA = qw(Tie::Hash);
+
sub DELETE { ... } # Provides needed method
sub CLEAR { ... } # Overrides inherited method
-
-
+
+
package NewStdHash;
require Tie::Hash;
-
- @ISA = (Tie::StdHash);
-
+
+ @ISA = qw(Tie::StdHash);
+
# All methods provided by default, define only those needing overrides
+ # Accessors access the storage in %{$_[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> package
-provides most methods required for hashes in L<perltie>. It inherits from
-B<Tie::Hash>, and causes tied hashes to behave exactly like standard hashes,
-allowing for selective overloading of methods. The C<new> method is provided
-as grandfathering in the case a class forgets to include a C<TIEHASH> method.
+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
+=over 4
=item TIEHASH classname, LIST
=item FIRSTKEY this
-Return the (key, value) pair for the first key in the hash.
+Return the first key in the hash.
=item NEXTKEY this, lastkey
-Return the next (key, value) pair for the hash.
+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>.
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 CAVEATS
+=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 L<perltie> documentation includes a method called C<DESTROY> as
-a necessary method for tied hashes. Neither B<Tie::Hash> nor B<Tie::StdHash>
-define a default for this method. This is a standard for class packages,
-but may be omitted in favor of a simple default.
+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 implemetations (F<DB_File>,
+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;
sub TIEHASH {
my $pkg = shift;
- if (defined &{"{$pkg}::new"}) {
- carp "WARNING: calling ${pkg}->new since ${pkg}->TIEHASH is missing"
- if $^W;
+ if (defined &{"${pkg}::new"}) {
+ warnings::warnif("WARNING: calling ${pkg}->new since ${pkg}->TIEHASH is missing");
$pkg->new(@_);
}
else {
# alter some parts of their behaviour.
package Tie::StdHash;
-@ISA = qw(Tie::Hash);
+# @ISA = qw(Tie::Hash); # would inherit new() only
sub TIEHASH { bless {}, $_[0] }
sub STORE { $_[0]->{$_[1]} = $_[2] }
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]} }
1;
projects / p5sagit/p5-mst-13.2.git / blobdiff