


Tie::Hash(3p)    Perl Programmers Reference Guide   Tie::Hash(3p)


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.




29/Apr/1999            perl 5.005, patch 03                     1





Tie::Hash(3p)    Perl Programmers Reference Guide   Tie::Hash(3p)


       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.






















29/Apr/1999            perl 5.005, patch 03                     2


