How do I create a 'reference' to a lambda?

Question

I want to capture a 'reference' to a lambda, and I thought that a function pointer would do the trick, as in:

int (*factorial)(int) = [&](int x){
    return (x < 2)
        ? 1
        : x * factorial(x - 1);
};

but I get cannot convert from main::lambda<......> to int(_cdecl *)(int).

What's the proper way to point to a lambda then?

Answer 1

Since the lambda is not stateless, it cannot be converted to a function pointer. Use std::function instead.

std::function<int(int)> factorial  = [&](int x){
  return (x < 2)
      ? 1
      : x * factorial(x - 1);
};

Answer 2

This would be closest to what you have already:

std::function<int (int)> factorial = [&](int x){
    return (x < 2)
        ? 1
        : x * factorial(x - 1);
};

normally you could also use auto, but in this case it doesn't work because the function is recursive.