Tie::Hash, Tie::StdHash - base class definitions for tied hashes
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';
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 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 perltie 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 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.
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.
The packages relating to various DBM-related implementations (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.
