Implementing generic map and reduce functions for certain collections in c++11 using lambda `std::function`

map.cpp

#include <iostream>
#include <vector>
#include <list>

template<typename T, typename V>
T map(T list, std::function<V (V)> fn) {
  T new_list;
  for(V& value : list) {
    new_list.push_back( fn(value) );
  }
  return new_list;
};

int main(int argc, const char * argv[]) {
  
  //
  // On a Vector
  //
  
  auto vector_of_ints = std::vector<int> { 1, 2, 3 };
  
  auto exp = map<std::vector<int>, int>( vector_of_ints, [](int val) {
    return val * val;
  });
  
  for(int val : exp) {
    std::cout << val << std::endl; //=> 1, 4, 9
  }
  
  //
  // Or a List
  //
  
  auto list_of_strings = std::list<std::string> { "hi", "hello", "me" };
  
  auto exp2 = map<std::list<std::string>, std::string>( list_of_strings, [](std::string val) {
    return val + val;
  });
  
  for(std::string val : exp2) {
    std::cout << val << std::endl; //=> "hihi", "hellohello", "meme"
  }
}

reduce.cpp

#include <iostream>
#include <vector>
#include <list>

template<typename T, typename V>
V reduce(T list, std::function<V (V, V)> fn) {
  V acc;
  bool assigned = false;
  for(V& value : list) {
    if(!assigned) {
      acc = value;
      assigned = true;
      continue;
    }
    
    acc = fn(acc, value);
  }
  return acc;
}

int main(int argc, const char * argv[]) {
  
  //
  // Now Reducing on the Vector
  //
  
  int reduction = reduce<std::vector<int>, int>(vector_of_ints, [](int acc, int val) {
    return acc + val;
  });
  
  std::cout << reduction << std::endl; //=> 6
  
  //
  // And Reduce the List of Strings
  //
  
  auto reduction2 = reduce<std::list<std::string>, std::string>(list_of_strings, [](std::string acc, std::string val) {
    return acc + val;
  });
  
  std::cout << reduction2 << std::endl; //=> "hihellome"
}