C++ Code Block Magic

main.cpp

// Need C++ 11
#include <functional>
#include <iostream>

class A {
 public:
  template <class F>
  auto operator-(const F &func) -> typename std::result_of<F()>::type {
    return func();
  }
};

#define BLOCK A() - [&]

int main() {
  int year = 1994;
  int age = BLOCK {
    int now = 2019;
    return now - year;
  };
  printf("%d\n", age);
  return 0;
}