boolean - Boolean support for Perl
This document describes boolean version 0.46.
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);
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 = ''; $false5 = '0';
Every other scalar value is true.
This module provides basic Boolean support, by defining two special objects: true
and false
.
When sharing data between programming languages, it is important to support the same group of basic types. In Perlish programming languages, these types include: Hash, Array, String, Number, Null and Boolean. Perl lacks native Boolean support.
Data interchange modules like YAML and JSON can now use boolean
to encodedecoderoundtrip Boolean values.
This module defines the following functions:
true
This function returns a scalar value which will evaluate to true. The value is a singleton object, meaning there is only one "true" value in a Perl process at any time. You can check to see whether the value is the "true" object with the isTrue function described below.
false
This function returns a scalar value which will evaluate to false. The value is a singleton object, meaning there is only one "false" value in a Perl process at any time. You can check to see whether the value is the "false" object with the isFalse function described below.
boolean($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.
Since true and false return objects, you can call methods on them.
$boolean->isTrue
Same as isTrue($boolean).
$boolean->isFalse
Same as isFalse($boolean).
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
This module offered an export tag, -truth
, that overrides the Perl interpreter's internal values for true and false. This has been found to corrupt the interpreter in some circumstances. Also, these overrides will no longer be possible as of Perl 5.22. Therefore, the -truth
import tag is deprecated.
JSON::MaybeXS (or less preferably JSON.pm ) will encode Perl data with boolean.pm values correctly if you use the convert_blessed
option:
use JSON::MaybeXS; use boolean -truth; my $json = JSON::MaybeXS->new->convert_blessed; say $json->encode({false => (0 == 1)}); # Says: '{"false":false}',
Ingy döt Net <ingy@cpan.org>
Copyright 2007-2016. Ingy döt Net.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.