illusionist illusionist - 6 months ago 47
Perl Question

Perl - Performing boolean operations on JSON::XS::Boolean

I am currently using the

to properly encode booleans into
format. Is there a way to perform boolean operations on these objects while preserving their ability to be encoded properly?

#!/usr/bin/env perl
use strict;
use warnings;

use JSON::XS::Boolean;

my $json = JSON::XS->new;

print($json->encode([JSON::XS::true])); # prints '[true]'
print($json->encode([!JSON::XS::false])); # prints ["1"] instead of '[false]'

Curiously, the
operators seem to behave properly:

print($json->encode([JSON::XS::false and JSON::XS::false])); # prints '[false]'
print($json->encode([JSON::XS::true && JSON::XS::true])); # prints '[true]'
print($json->encode([JSON::XS::false and JSON::XS::true])); # prints '[false]'

print($json->encode([JSON::XS::false || JSON::XS::false])); # prints '[false]'
print($json->encode([JSON::XS::true or JSON::XS::true])); # prints '[true]'
print($json->encode([JSON::XS::false || JSON::XS::true])); # prints '[true]'

Answer Source

To do what you want them to do, the objects returned by JSON::XS::true and JSON::XS::false would have to overload negation. They don't.

You could replace



$p ? JSON::XS::false : JSON::XS::true

Or you could normalize your data after the fact.

AND and OR happen to work because they always return one of their inputs.

Expression  Returns when  Returns when
            $p is true    $p is false
----------  ------------  ------------
$p || $q    $p            $q
$p && $q    $q            $p

A similar definition —one that returns an input— can't exist for NOT, so it returns a fresh value.

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