Readonly 1.03

Readonly is a Perl module that offers the facility for creating read-only scalars, arrays, hashes.

SYNOPSIS

use Readonly;

# Read-only scalar
Readonly::Scalar $sca => $initial_value;
Readonly::Scalar my $sca => $initial_value;

# Read-only array
Readonly::Array @arr => @values;
Readonly::Array my @arr => @values;

# Read-only hash
Readonly::Hash %has => (key => value, key => value, ...);
Readonly::Hash my %has => (key => value, key => value, ...);
# or:
Readonly::Hash %has => {key => value, key => value, ...};

# You can use the read-only variables like any regular variables:
print $sca;
$something = $sca + $arr[2];
next if $has{$some_key};

# But if you try to modify a value, your program will die:
$sca = 7;
push @arr, seven;
delete $has{key};
# The error message is "Modification of a read-only value
attempted"

# Alternate form (Perl 5.8 and later)
Readonly $sca => $initial_value;
Readonly my $sca => $initial_value;
Readonly @arr => @values;
Readonly my @arr => @values;
Readonly %has => (key => value, key => value, ...);
Readonly my %has => (key => value, key => value, ...);
# Alternate form (for Perls earlier than v5.8)
Readonly $sca => $initial_value;
Readonly my $sca => $initial_value;
Readonly @arr => @values;
Readonly my @arr => @values;
Readonly %has => (key => value, key => value, ...);
Readonly my %has => (key => value, key => value, ...);

This is a facility for creating non-modifiable variables. This is useful for configuration files, headers, etc. It can also be useful as a development and debugging tool, for catching updates to variables that should not be changed.
If any of the values you pass to Scalar, Array, or Hash are references, then those functions recurse over the data structures, marking everything as Readonly. Usually, this is what you want: the entire structure nonmodifiable. If you want only the top level to be Readonly, use the alternate Scalar1, Array1 and Hash1 functions.

Please note that most users of Readonly will also want to install a companion module Readonly::XS. See the "CONS" section below for more details.