Tie::Hash
See the current Perl documentation for Tie::Hash.
Here is our local, out-dated (pre-5.6) version:
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
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 methodsTIEHASH
,EXISTS
andCLEAR
. 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. Thenew
method is provided as grandfathering in the case a class forgets to include aTIEHASH
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.
- 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 implemetations (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.