hash.c:930
static int
rb_hash_update_block_i(key, value, hash)
    VALUE key, value;
    VALUE hash;
{
    if (key == Qundef) return ST_CONTINUE;
    if (rb_hash_has_key(hash, key)) {
	value = rb_yield_values(3, key, rb_hash_aref(hash, key), value);
    }
    rb_hash_aset(hash, key, value);
    return ST_CONTINUE;
}
