each_with_index

static VALUE
enumerator_with_index(VALUE obj)
{
    struct enumerator *e;
    VALUE memo = 0;
    int argc = 0;
    VALUE *argv = 0;

    RETURN_ENUMERATOR(obj, 0, 0);
    e = enumerator_ptr(obj);
    if (e->args) {
        argc = RARRAY_LEN(e->args);
        argv = RARRAY_PTR(e->args);
    }
    return rb_block_call(e->obj, e->meth, argc, argv,
                         enumerator_with_index_i, (VALUE)&memo);
}