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.IX Title "Tie::Scalar 3perl"
.TH Tie::Scalar 3perl 2024-02-11 "perl v5.38.2" "Perl Programmers Reference Guide"
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.SH NAME
Tie::Scalar, Tie::StdScalar \- base class definitions for tied scalars
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 2
\&    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, \*(AqNewScalar\*(Aq;
\&    tie $new_std_scalar, \*(AqNewStdScalar\*(Aq;
.Ve
.SH DESCRIPTION
.IX Header "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 \fBTie::Scalar\fR package provides a \f(CW\*(C`new\*(C'\fR method, as well
as methods \f(CW\*(C`TIESCALAR\*(C'\fR, \f(CW\*(C`FETCH\*(C'\fR and \f(CW\*(C`STORE\*(C'\fR. The \fBTie::StdScalar\fR
package provides all the methods specified in  perltie. It inherits from
\&\fBTie::Scalar\fR and causes scalars tied to it to behave exactly like the
built-in scalars, allowing for selective overloading of methods. The \f(CW\*(C`new\*(C'\fR
method is provided as a means of legacy support for classes that forget to
provide their own \f(CW\*(C`TIESCALAR\*(C'\fR method.
.PP
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:
.IP "TIESCALAR classname, LIST" 4
.IX Item "TIESCALAR classname, LIST"
The method invoked by the command \f(CW\*(C`tie $scalar, classname\*(C'\fR. Associates a new
scalar instance with the specified class. \f(CW\*(C`LIST\*(C'\fR would represent additional
arguments (along the lines of AnyDBM_File and compatriots) needed to
complete the association.
.IP "FETCH this" 4
.IX Item "FETCH this"
Retrieve the value of the tied scalar referenced by \fIthis\fR.
.IP "STORE this, value" 4
.IX Item "STORE this, value"
Store data \fIvalue\fR in the tied scalar referenced by \fIthis\fR.
.IP "DESTROY this" 4
.IX Item "DESTROY this"
Free the storage associated with the tied scalar referenced by \fIthis\fR.
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.
.SS "Tie::Scalar vs Tie::StdScalar"
.IX Subsection "Tie::Scalar vs Tie::StdScalar"
\&\f(CW\*(C`Tie::Scalar\*(C'\fR provides all the necessary methods, but one should realize
they do not do anything useful. Calling \f(CW\*(C`Tie::Scalar::FETCH\*(C'\fR or 
\&\f(CW\*(C`Tie::Scalar::STORE\*(C'\fR results in a (trappable) croak. And if you inherit
from \f(CW\*(C`Tie::Scalar\*(C'\fR, you \fImust\fR provide either a \f(CW\*(C`new\*(C'\fR or a
\&\f(CW\*(C`TIESCALAR\*(C'\fR method.
.PP
If you are looking for a class that does everything for you that you don't
define yourself, use the \f(CW\*(C`Tie::StdScalar\*(C'\fR class, not the
\&\f(CW\*(C`Tie::Scalar\*(C'\fR one.
.SH "MORE INFORMATION"
.IX Header "MORE INFORMATION"
The perltie section uses a good example of tying scalars by associating
process IDs with priority.