C++11 Lambdas

returning_function_as_function_result.cpp

#include <cassert>
#include <functional>

std::function<int()> create_counter(int const delta) {
  int counter = 0;
  return [delta, counter]() mutable {
    return counter += delta;
  };
}

int main() {
  auto by1counter = create_counter(1);
  auto by10counter = create_counter(10);
  assert(by1counter() == 1);
  assert(by1counter() == 2);
  assert(by10counter() == 10);
  assert(by10counter() == 20);
  assert(by1counter() == 3);
  assert(by10counter() == 30);
  assert(by1counter() == 4);
  assert(by10counter() == 40);
  auto by100counter = create_counter(100);
  assert(by100counter() == 100);
  assert(by1counter() == 5);
  assert(by100counter() == 200);
  assert(by10counter() == 50);
}