条款24：若所有参数皆需类型转换，请为此采用non-member函数

Rational class：

class Rational { pbulic: Rational(int numerator = 0, int denominator = 1); //注意这个构造函数不为explicit int numerator() const; int denominator() const; //两个接口 提供对成员的访问 priavte: .... };

 

1、member函数实现：

class Rational { public: ..... const Rational operator* (const Rational& rhs) const; };  

 

2、non-member函数实现：

class Rational { ... }; const Rational operator* (const Rational& lhs, const Rational& rhs) //一个non-member函数 { return Rational(lhs.numerator() * rhs.numerator(), lhs.denominator()* rhs.denominator()); }

 

针对以下代码：

 Rational oneHalf(1,2);
 Rational result = oneHalf * oneEighth; 
 result = oneHalf * 2;    //1与2都没错误
 result = 2 * oneHalf;    //1错误，2很好