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Manual Reference Pages  -  TIE::SCALAR (3)

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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 <B>Tie::ScalarB> package provides a new method, as well as methods TIESCALAR, FETCH and STORE. The <B>Tie::StdScalarB> package provides all the methods specified in perltie. It inherits from <B>Tie::ScalarB> 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.
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perl v5.22.1 TIE::SCALAR (3) 2015-10-17

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