NAME¶
Tie::Scalar, Tie::StdScalar - base class definitions for tied scalars
SYNOPSIS¶
package NewScalar;
require Tie::Scalar;
@ISA = qw(Tie::Scalar);
sub FETCH { ... } # Provide a needed method
sub TIESCALAR { ... } # Overrides inherited method
package NewStdScalar;
require Tie::Scalar;
@ISA = qw(Tie::StdScalar);
# All methods provided by default, so define
# only what needs be overridden
sub FETCH { ... }
package main;
tie $new_scalar, 'NewScalar';
tie $new_std_scalar, 'NewStdScalar';
DESCRIPTION¶
This module provides some skeletal methods for scalar-tying classes. See perltie
for a list of the functions required in tying a scalar to a package. The basic
Tie::Scalar package provides a "new" method, as well as
methods "TIESCALAR", "FETCH" and "STORE". The
Tie::StdScalar package provides all the methods specified in perltie.
It inherits from
Tie::Scalar and causes scalars tied to it to behave
exactly like the built-in scalars, allowing for selective overloading of
methods. The "new" method is provided as a means of grandfathering,
for classes that forget to provide their own "TIESCALAR" method.
For developers wishing to write their own tied-scalar classes, the methods are
summarized below. The perltie section not only documents these, but has sample
code as well:
- TIESCALAR classname, LIST
- The method invoked by the command "tie $scalar, classname".
Associates a new scalar instance with the specified class.
"LIST" would represent additional arguments (along the lines of
AnyDBM_File and compatriots) needed to complete the association.
- FETCH this
- Retrieve the value of the tied scalar referenced by this.
- STORE this, value
- Store data value in the tied scalar referenced by this.
- DESTROY this
- Free the storage associated with the tied scalar referenced by
this. This is rarely needed, as Perl manages its memory quite well.
But the option exists, should a class wish to perform specific actions
upon the destruction of an instance.
Tie::Scalar vs Tie::StdScalar¶
"Tie::Scalar" provides all the necessary methods, but one should
realize they do not do anything useful. Calling "Tie::Scalar::FETCH"
or "Tie::Scalar::STORE" results in a (trappable) croak. And if you
inherit from "Tie::Scalar", you
must provide either a
"new" or a "TIESCALAR" method.
If you are looking for a class that does everything for you you don't define
yourself, use the "Tie::StdScalar" class, not the
"Tie::Scalar" one.
The perltie section uses a good example of tying scalars by associating process
IDs with priority.