I have a vector of element V that needs to be sorted. I want to also produce a permutation vector P which reflects the element's position in the original vector. P is initialized with identity permutation (P[i] == i). 1st possibility: code my own sorting algorithm, and swap elements of P along with swapping elements of V. This I want to avoid, if at all possible. 2nd possibility: copy elements of V into new vector V' holding pair<T, size_t> and sort that. (pair holds the original element as well as its starting position in the vector, i.e. .second is again initialized to identity permutation.) Drawback: extra space and time spent on copying to V'. 3rd possibility: sort elements of P with less_than doing lookups into V to do its comparison. Drawback: while P holds the correct result, V is left unsorted; I have to do another pass through V and swap elements according to the permutation recorded in P, which is not trivial to do in-place. 4th possibility: I'm not sure whether it'd work: have a separate compilation unit that will provide function sort_vector_of_T, which will take references to V, T and also provide a specialization of std::swap for T which will then also swap elements of P). (Separate compilation unit is needed because I don't want to *globally* redefine std::swap for T) Is there some non-obvious, efficient and elegant way of achieving what I want?