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```{index} single: Tie::Scalar
```

# Tie::Scalar

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

## SYNOPSIS

```perl
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](https://perldoc.perl.org/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](https://perldoc.perl.org/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 legacy support 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](https://perldoc.perl.org/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](../AnyDBM_File.md) 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](https://perldoc.perl.org/perltie) section uses a good example of tying scalars by associating
process IDs with priority.