C++转换函数

class Fraction
{
public:
	Fraction(int num, int den = 1) : m_numerator(num), m_denominator(den) {}
	operator double() const
	{
		return (double)(m_numerator / m_denominator);
	}
private:
	int m_numerator;	//分子
	int m_denominator;	//分母
};

Fraction f(3, 5);
double d = 4 + f; //调用operator double() 将f转为 0.6