std :: mem_fun vs std :: mem_fn [英] std::mem_fun vs std::mem_fn

问题描述

std :: mem_fun 和 std :: mem_fn 之间有什么区别？为什么命名如此混乱？

What is the difference between std::mem_fun and std::mem_fn? Why is the naming so confusing?

Boost的文档说，在大多数情况下，std :: mem_fn可以替换std :: mem_fun。那么在什么情况下你仍然会使用std :: mem_fun？

Boost's documentation says that std::mem_fn can replace std::mem_fun in most cases. So in what situation would you still use std::mem_fun?

推荐答案

std :: mem_fun 已被弃用。 std :: mem_fn 可以做它做的一切，它做它更方便。两者之间的关系与 std :: bind1st / std :: bind2nd 和C ++ 11 std :: bind 。在 std ::后开发并掌握 std :: mem_fn 和 std :: bind bind1st 和 std :: mem_fun 被写入C ++ 98标准。所以这意味着我们必须等到C ++ 11才能用更好的替代方案来替换旧的东西。

std::mem_fun is deprecated. std::mem_fn can do everything it does, and it does it more conveniently. The relation between the two is the same as the relation between std::bind1st/std::bind2nd and the C++11 std::bind. Both std::mem_fn and std::bind were developed and mastered after std::bind1st and std::mem_fun were made into the C++98 Standard. So that means we had to wait until C++11 to properly replace the old stuff with the superior alternatives.

例如， std :: mem_fun 只能处理带有一个或没有参数的成员函数。 std :: mem_fn 是可变的，可以处理拥有任意数量参数的成员。

For instance, std::mem_fun can only deal with member functions that take one or no argument. std::mem_fn is variadic and can deal with members that take any number of arguments.

在 std :: mem_fun 和 std :: mem_fun_ref 之间选择取决于是否要处理指针或引用类对象（分别）。 std :: mem_fn 单独可以处理，甚至提供对智能指针的支持。

You also need to pick between std::mem_fun and std::mem_fun_ref depending on whether you want to deal with pointers or references for the class object (respectively). std::mem_fn alone can deal with either, and even provides support for smart pointers.

code> boost :: mem_fn 解释何时使用 std :: mem_fun ，简单地说，当你需要使用代码期望 std :: mem_fun ，或者期望可适应的函子（这是来自C ++ 03的过时的概念）。对于这些情况，你不能插入 std :: mem_fn ，所以你有它：你会使用 std :: mem_fun

The documentation of boost::mem_fn explains when to use std::mem_fun, and put simply that's when you need to operate with code that expects std::mem_fun, or that expects adaptable functors (which is an obsolete notion* from C++03). For those cases you wouldn't be able to plug in std::mem_fn either, so there you have it: you would use std::mem_fun for legacy.

*：我的意思是新代码不应该依赖于C ++ 03协议 result_type 成员类型（使用像 std :: result_of 这样的新特性更常见） std :: bind / std :: mem_fn 实际上提供那些成员，如果他们将存在于等效的C ++ 03代码。我离开它来确定你是否应该更新依赖于适应性函数与 std :: mem_fn 依靠此行为的旧代码。

*: I mean by that that new code shouldn't rely on the C++03 protocol of having e.g. result_type member types (it's more customary to use the new traits like std::result_of) -- the new facilities like std::bind/std::mem_fn do in fact provide those members if they would have been present in equivalent C++03 code. I leave it to you to figure out whether you should update old code that relies on adaptable functors with std::mem_fn by relying on this behaviour.

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