JSON::Ext::Generator::State#allow_duplicate_key?

static VALUE cState_allow_duplicate_key_p(VALUE self)
{
    GET_STATE(self);
    switch (state->on_duplicate_key) {
        case JSON_IGNORE:
            return Qtrue;
        case JSON_DEPRECATED:
            return Qnil;
        default:
            return Qfalse;
    }
}