重载操作符作为成员函数还是非成员（朋友）函数？ [英] Overload operators as member function or non-member (friend) function?

问题描述

我目前正在创建一个实用程序类，它将有重载的运算符。将它们成为成员或非成员（ friend ）的功能有什么利弊？还是有什么关系？

解决方案

每个操作符都有自己的注意事项。例如，<<运算符（当用于流输出，而不是位移位）获取一个ostream作为它的第一个参数，所以它不能是你的类的成员。如果您正在实施加法运算符，您可能希望从双方的自动类型转换中获益，因此您将与非会员一起使用等。

$对于允许通过继承进行专门化，通常的模式是根据虚拟成员函数（例如，操作符<调用正在传递的对象上的虚拟函数print（））来实现非成员运算符， 。

I am currently creating a utility class that will have overloaded operators in it. What are the pros and cons of either making them member or non-member (friend) functions? Or does it matter at all? Maybe there is a best practice for this?

解决方案

Each operator has its own considerations. For example, the << operator (when used for stream output, not bit shifting) gets an ostream as its first parameter, so it can't be a member of your class. If you're implementing the addition operator, you'll probably want to benefit from automatic type conversions on both sides, therefore you'll go with a non-member as well, etc...

As for allowing specialization through inheritance, a common pattern is to implement a non-member operator in terms of a virtual member function (e.g. operator<< calls a virtual function print() on the object being passed).

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