Perl 5 version 32.0 documentation

Tie::Scalar

NAME

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

SYNOPSIS

  1.     package NewScalar;
  2.     require Tie::Scalar;
  4.     @ISA = qw(Tie::Scalar);
  6.     sub FETCH { ... }		# Provide a needed method
  7.     sub TIESCALAR { ... }	# Overrides inherited method
  10.     package NewStdScalar;
  11.     require Tie::Scalar;
  13.     @ISA = qw(Tie::StdScalar);
  15.     # All methods provided by default, so define
  16.     # only what needs be overridden
  17.     sub FETCH { ... }
  20.     package main;
  22.     tie $new_scalar, 'NewScalar';
  23.     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 that you don't define yourself, use the Tie::StdScalar class, not the Tie::Scalar one.

MORE INFORMATION

The perltie section uses a good example of tying scalars by associating process IDs with priority.