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138 lines
3.2 KiB
138 lines
3.2 KiB
package Tie::Scalar;
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=head1 NAME
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Tie::Scalar, Tie::StdScalar - base class definitions for tied scalars
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=head1 SYNOPSIS
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package NewScalar;
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require Tie::Scalar;
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@ISA = (Tie::Scalar);
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sub FETCH { ... } # Provide a needed method
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sub TIESCALAR { ... } # Overrides inherited method
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package NewStdScalar;
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require Tie::Scalar;
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@ISA = (Tie::StdScalar);
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# All methods provided by default, so define only what needs be overridden
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sub FETCH { ... }
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package main;
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tie $new_scalar, 'NewScalar';
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tie $new_std_scalar, 'NewStdScalar';
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=head1 DESCRIPTION
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This module provides some skeletal methods for scalar-tying classes. See
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L<perltie> for a list of the functions required in tying a scalar to a
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package. The basic B<Tie::Scalar> package provides a C<new> method, as well
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as methods C<TIESCALAR>, C<FETCH> and C<STORE>. The B<Tie::StdScalar>
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package provides all the methods specified in L<perltie>. It inherits from
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B<Tie::Scalar> and causes scalars tied to it to behave exactly like the
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built-in scalars, allowing for selective overloading of methods. The C<new>
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method is provided as a means of grandfathering, for classes that forget to
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provide their own C<TIESCALAR> method.
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For developers wishing to write their own tied-scalar classes, the methods
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are summarized below. The L<perltie> section not only documents these, but
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has sample code as well:
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=over
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=item TIESCALAR classname, LIST
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The method invoked by the command C<tie $scalar, classname>. Associates a new
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scalar instance with the specified class. C<LIST> would represent additional
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arguments (along the lines of L<AnyDBM_File> and compatriots) needed to
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complete the association.
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=item FETCH this
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Retrieve the value of the tied scalar referenced by I<this>.
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=item STORE this, value
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Store data I<value> in the tied scalar referenced by I<this>.
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=item DESTROY this
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Free the storage associated with the tied scalar referenced by I<this>.
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This is rarely needed, as Perl manages its memory quite well. But the
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option exists, should a class wish to perform specific actions upon the
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destruction of an instance.
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=back
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=head1 MORE INFORMATION
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The L<perltie> section uses a good example of tying scalars by associating
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process IDs with priority.
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=cut
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use Carp;
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sub new {
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my $pkg = shift;
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$pkg->TIESCALAR(@_);
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}
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# "Grandfather" the new, a la Tie::Hash
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sub TIESCALAR {
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my $pkg = shift;
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if (defined &{"{$pkg}::new"}) {
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carp "WARNING: calling ${pkg}->new since ${pkg}->TIESCALAR is missing"
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if $^W;
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$pkg->new(@_);
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}
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else {
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croak "$pkg doesn't define a TIESCALAR method";
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}
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}
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sub FETCH {
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my $pkg = ref $_[0];
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croak "$pkg doesn't define a FETCH method";
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}
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sub STORE {
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my $pkg = ref $_[0];
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croak "$pkg doesn't define a STORE method";
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}
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#
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# The Tie::StdScalar package provides scalars that behave exactly like
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# Perl's built-in scalars. Good base to inherit from, if you're only going to
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# tweak a small bit.
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#
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package Tie::StdScalar;
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@ISA = (Tie::Scalar);
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sub TIESCALAR {
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my $class = shift;
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my $instance = shift || undef;
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return bless \$instance => $class;
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}
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sub FETCH {
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return ${$_[0]};
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}
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sub STORE {
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${$_[0]} = $_[1];
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}
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sub DESTROY {
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undef ${$_[0]};
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}
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1;
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