each_with_index

/*
 *  call-seq:
 *    e.with_index {|(*args), idx| ... }
 *    e.with_index
 *
 *  Iterates the given block for each elements with an index, which
 *  start from 0.  If no block is given, returns an enumerator.
 *
 */
static VALUE
enumerator_with_index(obj)
    VALUE obj;
{
    struct enumerator *e = enumerator_ptr(obj);
    VALUE memo = 0;
    int argc = 0;
    VALUE *argv = 0;

    RETURN_ENUMERATOR(obj, 0, 0);
    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);
}