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
functions 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::StdHash
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,
classname. Associates a new hash instance with the
specified class. LIST would represent additional
arguments (along the lines of the AnyDBM_File manpage
and compatriots) needed to complete the association.
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Tie::Hash(3) Perl Programmers Reference Guide Tie::Hash(3)
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.
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
implementations (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.
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