boolean(3) - Linux man page

Name

boolean - Boolean support for Perl

Synopsis

use boolean;

do &always if true;
do &never if false;

do &maybe if boolean($value)->isTrue;

and:

use boolean ':all';

$guess = int(rand(2)) % 2 ? true : false;

do &something if isTrue($guess);
do &something_else if isFalse($guess);

and:

use boolean -truth;

die unless ref(42 == 42) eq 'boolean';
die unless ("foo" =~ /bar/) eq '0';

Description

Most programming languages have a native "Boolean" data type. Perl does not.

Perl has a simple and well known Truth System. The following scalar values are false:

$false1 = undef;
$false2 = 0;
$false3 = 0.0;
$false4 = '';
$false5 = '0';

Every other scalar value is true.

This module provides basic Boolean support, by defining two special objects: "true" and "false".

Rationale

When sharing data between programming languages, it is important to support the same group of basic types. In Perlish programming languages, these types include: Hash, Array, String, Number, Null and Boolean. Perl lacks native Boolean support.

Data interchange modules like YAML and JSON can now "use boolean" to encode/decode/roundtrip Boolean values.

Functions

This module defines the following functions:

true: This function returns a scalar value which will evaluate to true. The value is a singleton object, meaning there is only one "true" value in a Perl process at any time. You can check to see whether the value is the "true" object with the isTrue function described below.
false: This function returns a scalar value which will evaluate to false. The value is a singleton object, meaning there is only one "false" value in a Perl process at any time. You can check to see whether the value is the "false" object with the isFalse function described below.
boolean($scalar): Casts the scalar value to a boolean value. If $scalar is true, it returns "boolean::true", otherwise it returns "boolean::false".
isTrue($scalar): Returns "boolean::true" if the scalar passed to it is the "boolean::true" object. Returns "boolean::false" otherwise.
isFalse($scalar): Returns "boolean::true" if the scalar passed to it is the "boolean::false" object. Returns "boolean::false" otherwise.
isBoolean($scalar): Returns "boolean::true" if the scalar passed to it is the "boolean::true" or "boolean::false" object. Returns "boolean::false" otherwise.

Methods

Since true and false return objects, you can call methods on them.

$boolean->isTrue: Same as isTrue($boolean).
$boolean->isFalse: Same as isFalse($boolean).

Use Options

By default this module exports the "true", "false" and "boolean" functions.

The module also defines these export tags:

:all: Exports "true", "false", "boolean", "isTrue", "isFalse", "isBoolean"

-truth

You can specify the "-truth" option to override truth operators to return "boolean" values. use boolean -truth; print ref("hello" eq "world"), "\n"; Prints: boolean "-truth" can be used with the other import options.

Author

Ingy doet Net <ingy@cpan.org>

Copyright

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

See http://www.perl.com/perl/misc/Artistic.html