function composition in C++ / C++11

Question

I am currently coding some cryptographic algorithms in C++11 that require a lot of function compositions. There are 2 types of composition I have to deal with :

Answer 1

A quick implementation of function iteration with argument forwarding. The helper type is unfortunately necessary because function templates can’t be partially specialised.

#include 
#include 
using namespace std;

template
struct iterate_helper {
  function f;
  iterate_helper(function f) : f(f) {}
  A operator()(A&& x) {
    return f(iterate_helper(f)(forward(x)));
  };
};

template
struct iterate_helper<1, A> {
  function f;
  iterate_helper(function f) : f(f) {}
  A operator()(A&& x) {
    return f(forward(x));
  };
};

template
function iterate(function f) {
  return iterate_helper(f);
}

int succ(int x) {
  return x + 1;
}

int main() {
  auto add5 = iterate<5>(function(succ));
  cout << add5(10) << '\n';
}