运算符重载和名称空间 [英] Operator overloading and namespaces

问题描述

可能重复:
非成员运算符重载应放在何处?

Possible Duplicate:
Where should non-member operator overloads be placed?

在SO上浏览时，我经常发现涉及超载/定义std::ostream& operator<<(std::ostream& os, const Foo& foo)或Foo operator+(const Foo& l, const Foo& r)的问题或答案.

While browsing on SO, I often find questions or answer that involves overloading/defining a std::ostream& operator<<(std::ostream& os, const Foo& foo) or a Foo operator+(const Foo& l, const Foo& r).

虽然我知道如何以及何时(不)编写这些运算符，但我对namespace感到困惑.

While I know how and when (not) to write these operators, I'm confused about the namespace thing.

如果我有以下课程:

namespace bar
{
  class Foo {};
}

我应该在哪个namespace中编写不同的运算符定义?

In which namespace should I write the different operator definitions ?

// Should it be this

namespace bar
{
  std::ostream& operator<<(std::ostream& os, const Foo& foo);
}

// Or this ?

namespace std
{
  ostream& operator<<(ostream& os, const bar::Foo& foo);
}

// Or this ?

std::ostream& operator<<(std::ostream& os, const bar::Foo& foo);

operator+也适用相同的问题.那么，这里的优良作法是什么?为什么?

The same question applies for the operator+. So, what is the good practice here and why ?

推荐答案

它应位于bar命名空间中.您必须考虑由什么构成类的接口，并将它们分组在一起.

It should be in the bar namespace. You must consider what makes up the interface for the class, and group those together.

类描述了一组数据以及对该数据进行操作的功能."您的自由功能在Foo上运行，因此它是Foo的一部分.应该在名称空间bar中将其与Foo分组.

"A class describes a set of data along with the functions that operate on that data." Your free function operates on a Foo, therefore it is part of Foo. It should be grouped with Foo in the namespace bar.

依赖于参数的查找(即ADL)将找到该功能.

Argument-dependent lookup, or ADL, will find the function.

我们也知道我们应该首选非朋友非成员功能.通常，这意味着您的类将具有其定义和成员函数，紧随其后的是对类进行操作的自由函数.

We also know that we should prefer non-friend non-member functions. What this means is that, in general, your classes will have their definition and member functions, followed immediately by free functions which operate on the class.

这篇关于运算符重载和名称空间的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！