Tie::Hash(h) Perl Programmers Reference GuideTie::Hash(h)



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 perltie 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 perltie. It
       inherits from Tie::Hash, and causes tied hashes to behave
       exactly like standard hashes, allowing for selective over-
       loading of methods. The "new" method is provided as grand-
       fathering 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
       perltie 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 AnyDBM_File 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.

           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 perltie 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 Config module. While these do not
       utilize Tie::Hash, they serve as good working examples.



perl v5.6.1                 2001-02-23           Tie::Hash(h)