Hi,

good suggestion, but unfortunately this gives me the same error as with fields.

Here is a example of the problem:

use Test::More;

use_ok('Data::Dumper');
use_ok('JSON');
{
    package Wrapper;
    use fields qw (
    _value
    );
    sub new{
        my $s = $_[0];
        unless (ref $s) {
            $s = fields::new($s);
        }
        $s->{_value} = 42;
        return $s;
    }
    sub TO_JSON{
        return $_[0]->{_value};
    }
}

my $t = Wrapper->new();
my $jsonString =  undef;
eval{
  my $json = JSON->new;
  $json->allow_nonref(1);
  $json->utf8(1);
  $json->convert_blessed(1);
  $json->allow_blessed(1);
  
  $jsonString = $json->encode($t);
};
if($@){
    print(Dumper($@));
    fail("We got an error");
}
print $jsonString;

done_testing();
[download]

ok 1 - use Data::Dumper;
#   Failed test 'We got an error'
ok 2 - use JSON;
$VAR1 = 'Modification of a read-only value attempted at /pathtofile/JS
+ON::XS-Fields.t line 34.
';
not ok 3 - We got an error
1..3
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