myvector.cpp

来自「很经典的书籍」· C++ 代码 · 共 82 行

//: C05:MyVector.cpp
// Optimizes away temporaries via templates
#include <cstddef>
#include <cstdlib>
#include <iostream>
using namespace std;

// A proxy class for sums of vectors
template<class, size_t> class MyVectorSum;

template<class T, size_t N>
class MyVector {
  T data[N];
public:
  MyVector<T,N>& operator=(const MyVector<T,N>& right) {
    for (size_t i = 0; i < N; ++i)
      data[i] = right.data[i];
    return *this;
  }
  MyVector<T,N>& operator=(const MyVectorSum<T,N>& right);
  const T& operator[](size_t i) const {
    return data[i];
  }
  T& operator[](size_t i) {
    return data[i];
  }
};
// Proxy class hold references; uses lazy addition
template <class T, size_t N>
class MyVectorSum {
  const MyVector<T,N>& left;
  const MyVector<T,N>& right;
public:
  MyVectorSum(const MyVector<T,N>& lhs,
              const MyVector<T,N>& rhs)
      : left(lhs), right(rhs) {}
  T operator[](size_t i) const {
    return left[i] + right[i];
  }
};
// Operator to support v3 = v1 + v2
template<class T, size_t N>
MyVector<T,N>&
MyVector<T,N>::operator=(const MyVectorSum<T,N>& right) {
  for (size_t i = 0; i < N; ++i)
    data[i] = right[i];
  return *this;
}
// operator+ just stores references
template<class T, size_t N>
inline MyVectorSum<T,N>
operator+(const MyVector<T,N>& left,
          const MyVector<T,N>& right) {
  return MyVectorSum<T,N>(left, right);
}
// Convenience functions for the test program below
template<class T, size_t N>
void init(MyVector<T,N>& v) {
  for (size_t i = 0; i < N; ++i)
    v[i] = rand() % 100;
}
template<class T, size_t N>
void print(MyVector<T,N>& v) {
  for (size_t i = 0; i < N; ++i)
    cout << v[i] << ' ';
  cout << endl;
}
int main() {
  MyVector<int, 5> v1;
  init(v1);
  print(v1);
  MyVector<int, 5> v2;
  init(v2);
  print(v2);
  MyVector<int, 5> v3;
  v3 = v1 + v2;
  print(v3);
  MyVector<int, 5> v4;
  // Not yet supported:
//!  v4 = v1 + v2 + v3;
} ///:~