Tie::Scalar(3pm) Perl Programmers Reference Guide Tie::Scalar(3pm)

Tie::Scalar, Tie::StdScalar - base class definitions for tied scalars

    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';

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:

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.
Retrieve the value of the tied scalar referenced by this.
Store data value in the tied scalar referenced by 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" 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 that 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.

2022-02-19 perl v5.34.1