c++ - 重载运算符 [ ] 用作 Polynomial 类的 setter

Question

我创建了一个 Polynomial 类，但我想重载索引运算符以用作 setter，例如 myPolyObject[0] = 2.5，但在尝试重载它时出现错误。

class Polynomial
{
public:
    Polynomial();
    Polynomial(Polynomial&);
    Polynomial(double* coefficient, int size);
    ~Polynomial() { delete [] polynomial ; }
    double operator [] (int exponent) const;
    friend ostream& operator << ( ostream& , const Polynomial&);
    Polynomial& operator = (const Polynomial&);
    double evaluate(double x) const;
    int getSize() const;
    double operator [] (int exponent, double coefficient);
    Polynomial& operator + ( Polynomial& );
    Polynomial& operator + ( double x );
    Polynomial& operator - (Polynomial&);
    Polynomial& operator - (double x);
    Polynomial& operator * (Polynomial&);
    Polynomial& operator * (double x);
private:
    double* polynomial;
};

在此代码中，我希望双运算符 [](整数指数， double 系数)为数组获取索引(指数)并将该索引处的值设置为 double 系数值。

Answer 1

你的问题好像想要两个不同的东西，第一位在评论里回答了，返回引用。这是完整性的示例，

struct example
{
    double value_[10];
    double& operator [] (int index) {
       return value_[index];
    }
};

int main() {
    example e;
    e[0] = 2.2;
    std::cout << e.value_[0] << std::endl;
}

Demo

然后你说..

I want double operator [] (int exponent, double coefficient) to take an index (exponent) for the array and set the value at that index to the double coefficient value.

你不能有 operator[]有多个参数。有几个选择；接受 std::pair<int,double> ，它的语法非常简洁。例如..

struct example
{
    double operator [] (const std::pair<int,double>& values) {
        return 2.0;
    }
};

int main() {
    example e;
    e[{1,2.2}];
    //or 
    e[std::make_pair(1,2.2)];
}

Demo

或者如果您真的想要逗号，您可以为指数创建自己的类型并重载逗号运算符。

struct exponent
{
    int exp_;
    double coeff_;
    exponent(int value) : exp_(value),coeff_(0){}

    operator std::pair<int,double>() {
        return std::make_pair(exp_,coeff_);
    }

    exponent& operator,(double coeff) {
        coeff_ = coeff;
        return *this;
    }
};

struct example
{
    double operator [] (const std::pair<int,double>& values) {
        return 2.0;
    }
};

int main() {
    example e;
    e[exponent(1), 3.3];
}

Demo

我个人会选择第一个选项，或者重载 operator()相反。