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.

     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 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.