比较函子类型与运算符< [英] Comparison Functor Types vs. operator<

问题描述

在 Google C ++风格指南中，运算符重载部分建议不要重载任何 运营商（罕见，特殊情况除外）。具体来说，它建议：

In the Google C++ Style Guide, the section on Operator Overloading recommends against overloading any operators ("except in rare, special circumstances"). Specifically, it recommends:

特别的，不要重载
operator == 或运算符< 只是为了
你的类可以用作
STL容器中的键;您应该在声明容器时
创建等价和比较函数
类型。

In particular, do not overload operator== or operator< just so that your class can be used as a key in an STL container; instead, you should create equality and comparison functor types when declaring the container.

小模糊的什么这样的函子会是什么样子，但我的主要问题是，为什么你想为此写自己的函子吗？不能定义运算符< ，并使用标准 std :: less< T> 函数，更简单？

I'm a little fuzzy on what such a functor would look like, but my main question is, why would you want to write your own functors for this? Wouldn't defining operator<, and using the standard std::less<T> function, be simpler? Is there any advantage to using one over the other?

推荐答案

除了更基本的类型，小于操作isn'总是微不足道，甚至平等可能因情况而异。

Except for the more fundamental types, the less-than operation isn't always trivial, and even equality may vary from situation to situation.

想象一下，想要为所有乘客分配登机号码的航空公司的情况。这个数字反映了登机的顺序（当然）。现在，什么决定谁谁谁？您可能只是按照客户注册的顺序 - 在这种情况下，小于操作将比较签入时间。您也可以考虑客户为其票证支付的价格 - 小于现在比较票价。

Imagine the situation of an airline that wants to assign all passengers a boarding number. This number reflects the boarding order (of course). Now, what determines who comes before who? You might just take the order in which the customers registered – in that case, the less-than operation would compare the check-in times. You might also consider the price customers paid for their tickets – less-than would now compare ticket prices.

...等等。总而言之，在 Passenger 类上定义运算符< 有乘客在被分类的容器。我认为这是Google警告的。

… and so on. All in all, it's just not meaningful to define an operator < on the Passenger class although it may be required to have passengers in a sorted container. I think that's what Google warns against.

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