我可以使用std :: pair，但重命名.first和.second成员名称吗？ [英] Can I use std::pair, but rename .first and .second member names?

问题描述

我遇到的一个常见设计问题是，我将两个变量捆绑在一起，然后失去了以有意义的方式引用它们的能力。

A common design problem I run into, is that I bundle two variables together and then lose the ability to reference them in a meaningful way.

std::pair<int,int> cords;
cord.first = 0; //is .first the x or y coordinate?
cord.second = 0; //is .second the x or y coordinate?

我曾经考虑编写基本结构，但随后我却失去了很多好处与 std :: pair ：

I've considered writing basic structs instead, but then I lose a lot of the benefits that come along with std::pair:

• make_pair


• 非成员重载运算符


• 交换


• 获取


• 等。

• make_pair
• non-member overloaded operators
• swap
• get
• etc.

是否可以重命名或提供 first 和第二个数据成员？

Is there a way to rename or provide an alternative identifier for the first and second data members?

我希望利用所有接受<$ c的功能$ c> std :: pair ，

，但仍然可以通过以下方式使用它们：

I was hoping to leverage all of the the functions that accept std::pair,
but still be able to use them in the following way:

std::pair<int,int> cords;  
//special magic to get an alternative name of access for each data member.

//.first and .second each have an alternative name.
cords.x = 1;
assert(cords.x == cords.first);

推荐答案

解决这个问题的一种方法是使用< a href = http://en.cppreference.com/w/cpp/utility/tuple/tie rel = noreferrer> std :: tie 。您可以 tie（）返回已命名的变量，以便使用好名字。

One way you could get around this is to use std::tie. You can tie() the return into variables that you have named so that you have good names.

int x_pos, y_pos;

std::tie(x_pos, y_pos) = function_that_returns_pair_of_cords();

// now we can use x_pos and y_pos instead of pair_name.first and pair_name.second

这的另一个好处是，如果您更改了函数以返回元组 tie（）也可以使用该功能。

Another benefit with this is if you ever change the function to return a tuple tie() will also work with that.

使用C ++ 17，我们现在有了结构化绑定，它允许您声明多个变量并将其绑定到函数的返回。这适用于数组，类似对象的元组/对和结构/类（只要它们满足某些要求）。在这种情况下使用结构化绑定，可以将上面的示例转换为

With C++17 we now have structured bindings which allow you to declare and bind multiple variables to the return of the function. This work with arrays, tuple/pair like objects and struct/classes (as long as they meet some requirments). Using structured bindings in this case lets use convert the above example into

auto [x_pos, y_pos] = function_that_returns_pair_of_cords();

您也可以这样做

auto& [x_pos, y_pos] = cords;

，现在 x_pos 是对 cords.first 和 y_pos 是对 cords.second 的引用

and now x_pos is a reference to cords.first and y_pos is a reference to cords.second.

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