return mrb_str_new_lit(mrb, "");

}

/* Get separator string */

const char *sep_ptr = "";

mrb_int sep_len = 0;

if (!mrb_nil_p(separator)) {

sep_ptr = RSTRING_PTR(separator);

sep_len = RSTRING_LEN(separator);

}

/* Create result string */

mrb_value result = mrb_str_new_capa(mrb, 64); /* Initial capacity */

mrb_bool first = TRUE;

int ai = mrb_gc_arena_save(mrb);

KSET_FOREACH(set, k) {

if (!first) {

mrb_str_cat(mrb, result, sep_ptr, sep_len);

if (!mrb_nil_p(separator)) {

mrb_str_cat(mrb, result, RSTRING_PTR(separator), RSTRING_LEN(separator));

}

}

else {

first = FALSE;