/usr/share/perl/5.22.1/Tie/Scalar.pm is in perl-modules-5.22 5.22.1-9ubuntu0.6.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 | package Tie::Scalar;
our $VERSION = '1.03';
=head1 NAME
Tie::Scalar, Tie::StdScalar - base class definitions for tied scalars
=head1 SYNOPSIS
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';
=head1 DESCRIPTION
This module provides some skeletal methods for scalar-tying classes. See
L<perltie> for a list of the functions required in tying a scalar to a
package. The basic B<Tie::Scalar> package provides a C<new> method, as well
as methods C<TIESCALAR>, C<FETCH> and C<STORE>. The B<Tie::StdScalar>
package provides all the methods specified in L<perltie>. It inherits from
B<Tie::Scalar> and causes scalars tied to it to behave exactly like the
built-in scalars, allowing for selective overloading of methods. The C<new>
method is provided as a means of grandfathering, for classes that forget to
provide their own C<TIESCALAR> method.
For developers wishing to write their own tied-scalar classes, the methods
are summarized below. The L<perltie> section not only documents these, but
has sample code as well:
=over 4
=item TIESCALAR classname, LIST
The method invoked by the command C<tie $scalar, classname>. Associates a new
scalar instance with the specified class. C<LIST> would represent additional
arguments (along the lines of L<AnyDBM_File> and compatriots) needed to
complete the association.
=item FETCH this
Retrieve the value of the tied scalar referenced by I<this>.
=item STORE this, value
Store data I<value> in the tied scalar referenced by I<this>.
=item DESTROY this
Free the storage associated with the tied scalar referenced by I<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.
=back
=head2 Tie::Scalar vs Tie::StdScalar
C<< Tie::Scalar >> provides all the necessary methods, but one should realize
they do not do anything useful. Calling C<< Tie::Scalar::FETCH >> or
C<< Tie::Scalar::STORE >> results in a (trappable) croak. And if you inherit
from C<< Tie::Scalar >>, you I<must> provide either a C<< new >> or a
C<< TIESCALAR >> method.
If you are looking for a class that does everything for you you don't
define yourself, use the C<< Tie::StdScalar >> class, not the
C<< Tie::Scalar >> one.
=head1 MORE INFORMATION
The L<perltie> section uses a good example of tying scalars by associating
process IDs with priority.
=cut
use Carp;
use warnings::register;
sub new {
my $pkg = shift;
$pkg->TIESCALAR(@_);
}
# "Grandfather" the new, a la Tie::Hash
sub TIESCALAR {
my $pkg = shift;
my $pkg_new = $pkg -> can ('new');
if ($pkg_new and $pkg ne __PACKAGE__) {
my $my_new = __PACKAGE__ -> can ('new');
if ($pkg_new == $my_new) {
#
# Prevent recursion
#
croak "$pkg must define either a TIESCALAR() or a new() method";
}
warnings::warnif ("WARNING: calling ${pkg}->new since " .
"${pkg}->TIESCALAR is missing");
$pkg -> new (@_);
}
else {
croak "$pkg doesn't define a TIESCALAR method";
}
}
sub FETCH {
my $pkg = ref $_[0];
croak "$pkg doesn't define a FETCH method";
}
sub STORE {
my $pkg = ref $_[0];
croak "$pkg doesn't define a STORE method";
}
#
# The Tie::StdScalar package provides scalars that behave exactly like
# Perl's built-in scalars. Good base to inherit from, if you're only going to
# tweak a small bit.
#
package Tie::StdScalar;
@ISA = qw(Tie::Scalar);
sub TIESCALAR {
my $class = shift;
my $instance = shift || undef;
return bless \$instance => $class;
}
sub FETCH {
return ${$_[0]};
}
sub STORE {
${$_[0]} = $_[1];
}
sub DESTROY {
undef ${$_[0]};
}
1;
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