


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 func-
       tions 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::Std-
       Hash 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, class-
           name". Associates a new hash instance with the speci-
           fied class. "LIST" would represent additional argu-
           ments (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.



2001-05-24                 perl v5.6.1                          1





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


       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.

           The Tie::Hash implementation is a stub that simply
           croaks.

       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 implementa-
       tions (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.






















2001-05-24                 perl v5.6.1                          2


