#!perl -l

use 5.012; # strict, //
use warnings;
use JSON 4.0;
use Data::Dumper;

select STDERR;

print $JSON::VERSION;

my $json_text = q({"flag":true});
my $json = JSON->new;
my $json_perl = $json->decode($json_text);
print "Before boolean_values = ", Dumper($json_perl);
$json->boolean_values(0,1);
my $json_perl_after = $json->decode($json_text);
print "After boolean_values = ", Dumper($json_perl_after);

__END__

4.02
Before boolean_values = $VAR1 = {
          'flag' => bless( do{\(my $o = 1)}, 'JSON::PP::Boolean' )
        };

After boolean_values = $VAR1 = {
          'flag' => 1
        };