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  1. #include <iostream>
  2. #include <limits>
  3.  
  4. #define WRAPPER(Name, defaultValue, maxValue) \
  5. template <class T> \
  6. struct Name { \
  7.     T value; \
  8.     constexpr inline Name(const T& value = defaultValue) : value(value) {} \
  9.     explicit inline operator T() const { return value; } \
  10.     explicit inline operator bool() const { return value != defaultValue; }
  11.  
  12. WRAPPER(Assign, -std::numeric_limits<T>::max(), std::numeric_limits<T>::max())
  13.     inline void operator += (const Assign& other) {
  14.         if (other) value = other.value;
  15.     }
  16.     friend inline Assign operator + (const Assign& lhs, const Assign& rhs) {
  17.         return rhs.value;
  18.     }
  19. };
  20.  
  21. WRAPPER(Sum, 0, std::numeric_limits<T>::max() / 2)
  22.     inline void operator += (const Sum& other) { value += other.value; }
  23.     inline void operator += (const Assign<T>& other) {
  24.         if (other) value = other.value;
  25.     }
  26.     friend inline Sum operator + (const Sum& lhs, const Sum& rhs) {
  27.         return lhs.value + rhs.value;
  28.     }
  29. };
  30.  
  31. int main() {
  32.     Sum<int> sum(2);
  33.     sum += Sum<int>(3);
  34.     std::cout << (int)sum << std::endl;
  35.     sum += Assign<int>(4);
  36.     std::cout << (int)sum << std::endl;
  37.     return 0;
  38. }
  39.  
Success #stdin #stdout 0s 16048KB
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https://ideone.com/7yQH6L
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
secret

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