Tie::Hash(3) Perl Programmers Reference Guide Tie::Hash(3)NAME
Tie::Hash, Tie::StdHash - base class definitions for tied
hashes
SYNOPSIS
package NewHash;
require Tie::Hash;
@ISA = (Tie::Hash);
sub DELETE { ... } # Provides needed method
sub CLEAR { ... } # Overrides inherited method
package NewStdHash;
require Tie::Hash;
@ISA = (Tie::StdHash);
# All methods provided by default, define only those needing overrides
sub DELETE { ... }
package main;
tie %new_hash, 'NewHash';
tie %new_std_hash, 'NewStdHash';
DESCRIPTION
This module provides some skeletal methods for hash-tying
classes. See the perltie manpage for a list of the func
tions required in order to tie a hash to a package. The
basic Tie::Hash package provides a "new" method, as well
as methods "TIEHASH", "EXISTS" and "CLEAR". The Tie::Std
Hash package provides most methods required for hashes in
the perltie manpage. It inherits from Tie::Hash, and
causes tied hashes to behave exactly like standard hashes,
allowing for selective overloading of methods. The "new"
method is provided as grandfathering in the case a class
forgets to include a "TIEHASH" method.
For developers wishing to write their own tied hashes, the
required methods are briefly defined below. See the the
perltie manpage section for more detailed descriptive, as
well as example code:
TIEHASH classname, LIST
The method invoked by the command "tie %hash, class
name". Associates a new hash instance with the speci
fied class. "LIST" would represent additional argu
ments (along the lines of the AnyDBM_File manpage and
compatriots) needed to complete the association.
STORE this, key, value
Store datum value into key for the tied hash this.
FETCH this, key
Retrieve the datum in key for the tied hash this.
FIRSTKEY this
Return the (key, value) pair for the first key in the
hash.
NEXTKEY this, lastkey
Return the next key for the hash.
EXISTS this, key
Verify that key exists with the tied hash this.
The Tie::Hash implementation is a stub that simply
croaks.
DELETE this, key
Delete the key key from the tied hash this.
CLEAR this
Clear all values from the tied hash this.
CAVEATS
The the perltie manpage documentation includes a method
called "DESTROY" as a necessary method for tied hashes.
Neither Tie::Hash nor 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.
MORE INFORMATION
The packages relating to various DBM-related implementa
tions (DB_File, NDBM_File, etc.) show examples of general
tied hashes, as does the the Config manpage module. While
these do not utilize Tie::Hash, they serve as good working
examples.
2001-02-22 perl v5.6.1 Tie::Hash(3)
