vector map

generic_vector_map.cpp

template<typename T>
struct vector { int length; T* data; };

using vector_int = vector<int>;
using vector_float = vector<float>;

// F is a function type that takes T and returns R
// Map takes a vector<T>, and F and returns vector<R>
template<class T, class F>
auto Map(vector<T> input, F func){
  using R = decltype(func(input.data[0]));
  vector<R> result { input.length, new R[input.length] };
  for(int i=0; i < input.length; i++)
    result.data[i] = func(input.data[i]);
  return result;
}


#include <math.h>
#include <stdio.h>
int main() {
  vector_int ivec { 5, new int[5] {1, 2, 3, 4, 5} };
  vector_float fvec = Map(ivec, sqrtf);
  for(int i = 0; i < fvec.length; i++)
    printf("%d -> %f\n", i, fvec.data[i]);
}

specialized_vector_map.cpp

struct vector_int { int length; int * data; };
struct vector_float { int length; float * data; };

// type_level function : vector_of<float>::type = vector_float etc.
template<typename T> struct vector_of { };
template<> struct vector_of<float> { using type = vector_float; };
template<> struct vector_of<int>   { using type = vector_int; };

// TCollection has .length and array of T .data
// F is a function taking T and returning R
// Map takes a TCollectoin and F and returns a vector of Rs
template<class TCollection, class F>
auto Map(TCollection input, F func){
  using R = decltype(func(input.data[0]));
  using vector_of_R = typename vector_of<R>::type;
  vector_of_R result { input.length, new R[input.length] };
  for(int i=0; i < input.length; i++)
    result.data[i] = func(input.data[i]);
  return result;
}

#include <math.h>
#include <stdio.h>
int main() {
  vector_int ivec { 5, new int[5] {1, 2, 3, 4, 5} };
  vector_float fvec = Map(ivec, sqrtf);
  for(int i = 0; i < fvec.length; i++)
    printf("%d -> %f\n", i, fvec.data[i]);
}