/ 
Const-XS-0.14
River stage two • 4 direct dependents • 16 total dependents
/ Const::XS

NAME

Const::XS - Facility for creating read-only scalars, arrays, hashes

VERSION

Version 0.14

SYNOPSIS

package MyApp::Constants;

use Const::XS qw/const/;

use base 'Import::Export';

our %EX = (
	'$SCALAR' => [qw/all/],
	'@ARRAY' => [qw/all/],
	'%HASH' => [qw/all/],
);

const our $SCALAR => 'Hello World';
const our @ARRAY => qw/welcome to paradise/;
const our %HASH => ( one => 1, two => [ ... ], three => { ... }, four => sub { } );

1;

...

package MyApp::Controller::Logic;

use MyApp::Constants qw/$SCALAR @ARRAY %HASH/;

...

1;

EXPORTS

const

This is the one of four functions of this module. It takes a scalar, array or hash lvalue as the first argument, and a list of one or more values depending on the type of the first argument as the value for the variable. It will set the variable to that value and subsequently make it readonly. Arrays and hashes will be made deeply readonly.

const my %factory => (
	workers => 5,
	cb => sub { ... }
);

$factory{workers}; # 5;
$factory{cb}->();

$factory{not_set}; # errors
exists $factory{not_set}; # false

make_readonly

The second function exported by this module is make_readonly. It will take a perl variable or reference and make it readonly.

my $string = "abc";
make_readonly($string);
$string = 'def'; # errors

my $ref = { a => 1, b => 2, c => 3 };
make_readonly($ref);
$ref->{d}; # errors
$ref = { new => 1 }; # errors

Please note that if you call make_readonly on struct directly it will make that struct readonly however it is 'copied' into the variable and that does not get set as readonly. Take the following example.

my $ref = make_readonly({a => 1, b => 2, c => 3 }; # we copy into $ref
$ref->{d}; # errors
$ref = { new => 1 };  # is okay

unmake_readonly

The third function exported by this module is unmake_readonly. It will take a perl variable that has been through make_readonly and deeply make it writeable again.

my $string = "abc";
make_readonly($string);
$string = 'def'; # errors
unmake_readonly($string);
$string = 'def'; # is okay

is_readonly

The fourth function exported by this module is is_readonly. It will deeply check a reference to see if it is readonly.

my $ref = { one => "abc" };
is_readonly($ref); # 0;
make_readonly($ref);
is_readonly($ref); # 1;

NOTE: this function fails to validate make_readonly scalar variables I am currently unsure why.

BENCHMARK

use Benchmark qw(:all);
use Const::Fast;
use Const::XS;
use Readonly;

timethese(5000000, {
	'Readonly' => sub {
		Readonly my $string => "Hello World";
		Readonly my %hash => (
			a => 1,
			b => 2,
			c => 3
		);
		Readonly my @array => (
			qw/1 2 3/
		);
	},
	'Const::Fast' => sub {
		Const::Fast::const my $string => "Hello World";
		Const::Fast::const my %hash => (
			a => 1,
			b => 2,
			c => 3
		);
		Const::Fast::const my @array => (
			qw/1 2 3/
		);
	},
	'XS' => sub {
		Const::XS::const my $string => "Hello World";
		Const::XS::const my %hash => (
			a => 1,
			b => 2,
			c => 3
		);
		Const::XS::const my @array => (
			qw/1 2 3/
		);
	}
});

...

Benchmark: timing 5000000 iterations of Const::Fast, Readonly, XS...
Const::Fast: 18 wallclock secs (19.00 usr +  0.00 sys = 19.00 CPU) @ 263157.89/s (n=5000000)
  Readonly: 20 wallclock secs (19.77 usr +  0.01 sys = 19.78 CPU) @ 252780.59/s (n=5000000)
	XS:  4 wallclock secs ( 3.31 usr +  0.03 sys =  3.34 CPU) @ 1497005.99/s (n=5000000)

AUTHOR

LNATION, <email at lnation.org>

BUGS

Please report any bugs or feature requests to bug-const-xs at rt.cpan.org, or through the web interface at https://rt.cpan.org/NoAuth/ReportBug.html?Queue=Const-XS. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

SUPPORT

You can find documentation for this module with the perldoc command.

perldoc Const::XS

You can also look for information at:

ACKNOWLEDGEMENTS

LICENSE AND COPYRIGHT

This software is Copyright (c) 2025 by LNATION.

This is free software, licensed under:

The Artistic License 2.0 (GPL Compatible)