How to make the lambda a friend of a class?

Question

Let\'s say, I have a class:

class A {
  int a;
};

And I have a lambda:

auto function = [](A* a) {
  a->a;  // <== giv         


        

Answer 1

You can do it by creating a friend function that returns the lambda function. It inherits the friend access:

struct A {
  friend std::function f();

  private:
    int i;
    void test() {std::cout << "test: " << i << "\n";}
};

std::function f() {
  return [] (A &a, int i) {a.i = i; a.test(); };
}

int main() {
    A a;
    f()(a, 13);

    return 0;
}