依然是对more effective c＋＋条款30－Proxy Class的学习笔记。
#include
using namespace std;
template
class Array
{
public:
class Proxy
{
public:
Proxy(Array& array, int index)
: theArray(array), itemIndex(index)
{}
Proxy& operator = (const T& rhs)
{
theArray.array[itemIndex] = rhs;
return *this;
}
operator T() const
{
return theArray.array[itemIndex];
}
private:
Array& theArray;
int itemIndex;
};
const Proxy operator[](int index) const;
Proxy operator[](int index);
friend class Proxy;
Array(int dim);
~Array();
private:
T* array;
};
template
Array::Array(int dim)
{
array = new T[dim];
}
template
Array::~Array()
{
delete [] array;
}
template
Array::Proxy Array::operator[](int index)
{
return Proxy(*this, index);
}
template
const Array::Proxy Array::operator [] (int index) const
{
return Proxy(const_cast(*this), index);}class Rational{public: Rational(int numerator = 0, int denominator = 1); int numerator() const; int denominator() const; friend ostream& operator<<(ostream& os, const Rational& rhs);private: int num; int deno;};Rational::Rational(int numerator, int denominator): num(numerator), deno(denominator){ std::cout << "Rational Construct" << std::endl;}int Rational::numerator() const{ std::cout << "numerator" << std::endl; return 0;}int Rational::denominator() const{ std::cout << "denominator" << std::endl; return 0;}ostream& operator<<(ostream& os, const Rational& rhs){ os << rhs.num << " " << rhs.deno; return os;}int main(){ Array a(5); a[1].numerator(); //错误}之所以出现错误的原因是：operator[] 返回一个代理对象而不是实际的Rational对象。但成员函数numerator()和denominator()只存在于Rational对象上，而不是其代理对象。但是我想，为什么编译器在这里不调用隐式转换函数 operator T() const { return theArray.array[itemIndex]; }呢？如果调用了，那么错误也就应该不会出现了一个简单的解决办法是int main(){ Array a(5); (( Rational ) a[1] ).numerator(); }