the new real length of some contiguous datastructure using strategy strat given new virtual length new_len. The user should then use this new real length to resize the datastructure.
Be careful, the new (real) length must be larger than the new virtual length, otherwise your program will crash!
the new real length of a resizable datastructure given its current real length real_len and its required new virtual length new_len wrt. strategy strat. The user should then use this new real length to resize the datastructure. If -1 is returned, it is not necessary to resize.
Be careful, the new (real) length must be larger than the new virtual length new_len, otherwise your program may crash!