Effective C + + clause 24

If all parameters require type conversion, use the Non-member function for this

We went straight to the subject
If you define a rational number class as follows

class Rational{public:    Rational(int numerator=0int denominator=1);//非explicit，允许隐式转换    constoperator*(const Rational& rhs);      .......................};result=oneHalf*2;//正确，相当于oneHalf.operator*(2);result=2*oneHalf;//错误，相当于2.operator*(oneHalf);

We can see result=2*oneHalf; that this sentence cannot be compiled because the compiler does not find much such a function. Then why does result=oneHalf*2; this sentence get compiled? This is because the class rational at this time can be implicitly converted.

To be able to execute result=2*oneHalf; this sentence, we can define a non-member function, as follows

constoperator*(constconst Rational& rhs);result=oneHalf*2;//正确，相当于operator*(oneHalf,Rational temp(2));result=2*oneHalf;//正确，相当于operator*(Rational temp(2),oneHalf);

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Effective C + + clause 24