box1.cpp

来自「很经典的书籍」· C++ 代码 · 共 37 行

//: C05:Box1.cpp
// Defines template operators
#include <iostream>
using namespace std;
// Forward declarations
template<class T>
class Box;
template<class T>
Box<T> operator+(const Box<T>&, const Box<T>&);
template<class T>
ostream& operator<<(ostream&, const Box<T>&);

template<class T>
class Box {
  T t;
public:
  Box(const T& theT) : t(theT) {}
  friend Box operator+<>(const Box<T>&, const Box<T>&);
  friend ostream& operator<< <>(ostream&, const Box<T>&);
};

template<class T>
Box<T> operator+(const Box<T>& b1, const Box<T>& b2) {
  return Box<T>(b1.t + b2.t);
}

template<class T>
ostream& operator<<(ostream& os, const Box<T>& b) {
  return os << '[' << b.t << ']';
}

int main() {
  Box<int> b1(1), b2(2);
  cout << b1 + b2 << endl;  // [3]
//  cout << b1 + 2 << endl; // no implicit conversions!
} ///:~