Tie::Hash(3)							  Tie::Hash(3)

NAME    [Toc]    [Back]

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

SYNOPSIS    [Toc]    [Back]

	 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    [Toc]    [Back]

     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.




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Tie::Hash(3)							  Tie::Hash(3)



     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    [Toc]    [Back]

     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    [Toc]    [Back]

     The packages relating to various DBM-related implemetations (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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