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.

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, value) pair 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 implemetations (DB_File, NDBM_File, etc.) show examples of general tied hashes, as does the Config module. While these do not utilize Tie::Hash, they serve as good working examples.