命名空间和操作符在C ++中重载 [英] Namespaces and Operator Overloading in C++

问题描述

在特定命名空间中创建库时，为该命名空间中的类提供重载运算符通常很方便。看起来（至少用g ++）重载的操作符可以在库的命名空间中实现：

When authoring a library in a particular namespace, it's often convenient to provide overloaded operators for the classes in that namespace. It seems (at least with g++) that the overloaded operators can be implemented either in the library's namespace:

namespace Lib {
class A {
};

A operator+(const A&, const A&);
} // namespace Lib

或全局命名空间

namespace Lib {
class A {
};
} // namespace Lib

Lib::A operator+(const Lib::A&, const Lib::A&);

从我的测试，他们似乎都很好。这两个选项之间有什么实际区别吗？是否更好？

From my testing, they both seem to work fine. Is there any practical difference between these two options? Is either approach better?

推荐答案

您应该在库命名空间中定义它们。
编译器将通过参数依赖查找找到它们。

You should define them in the library namespace. The compiler will find them anyway through argument dependant lookup.

不需要污染全局命名空间。

No need to pollute the global namespace.

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