（Re）命名为std :: pair成员 [英] (Re)named std::pair members

问题描述

我不想写 town->第一个，而是写下 town-> name 。内联命名访问器（重命名地图迭代器的第一个和第二个和命名std ::对成员）是我迄今为止找到的最好的解决方案。我的命名访问器的问题是类型安全的损失：
pair< int，double> 可以指 struct {int index;双值; } 或 struct {int population; double avg_temp; } 。任何人都可以提出一个简单的方法，或许是类似traits的东西？

Instead of writing town->first I would like to write town->name. Inline named accessors (Renaming first and second of a map iterator and Named std::pair members) are the best solutions I have found so far. My problem with named accessors is the loss of type safety: pair<int,double> may refer to struct { int index; double value; } or to struct { int population; double avg_temp; }. Can anyone propose a simple approach, perhaps something similar to traits?

我经常想从一个函数返回一个对或一个元组，类型如 struct city {string name; int zipcode; } 和它的ctor。我很高兴了解boost和C ++ 0x，但我需要一个纯C ++ 03解决方案，而不增强。

I often want to return a pair or a tuple from a function and it is quite tiring to introduce a new type like struct city { string name; int zipcode; } and its ctor every time. I am thrilled to learn about boost and C++0x but I need a pure C++03 solution without boost.

更新

Re andrewdski的问题：是，一个（假设的）语法如 pair< int = index，double = value> 从 pair< int = population，double = avg_temp> 创建不同类型将满足您的要求。我甚至不介意必须实现一个自定义的对/元组模板类ONCE，并只是传递一个'名称traits'模板参数适当地，当我需要一个新的类型。我不知道'名称特征'会是什么样子。也许不可能。

Re andrewdski's question: yes, a (hypothetical) syntax like pair<int=index, double=value> which would create a distinct type from pair<int=population, double=avg_temp> would meet your requirement. I do not even mind having to implement a custom pair/tuple template class ONCE and just passing a 'name traits' template argument to it approprietly when I need a new type. I have no idea how that 'name traits' would look like. Maybe it's impossible.

推荐答案

我看不到你能做得比

struct city { string name; int zipcode; };

没有什么非必要的。你需要两个成员的类型，你的整个问题是给两个成员的名字，你希望它是一个独特的类型。

There's nothing non-essential there. You need the types of the two members, your whole question is predicated around giving names to the two members, and you want it to be a unique type.

你知道关于聚合初始化语法，对吧？你不需要一个构造函数或析构函数，编译器提供的函数很好。

You do know about aggregate initialization syntax, right? You don't need a constructor or destructor, the compiler-provided ones are just fine.

示例： http://ideone.com/IPCuw

Example: http://ideone.com/IPCuw

要求您引入新类型，否则 pair< string，int> 在（name，zipcode）和（population，temp）之间是不明确的。

Type safety requires that you introduce new types, otherwise pair<string, int> is ambiguous between (name, zipcode) and (population, temp).

在C ++ 03中，返回一个新的元组需要：

In C++03, returning a new tuple requires either:

city retval = { "name", zipcode };
return retval;

或写一个方便的构造函数：

or writing a convenience constructor:

city::city( std::string newName, int newZip ) : name(newName), zipcode(newZip) {}

获取

return city("name", zipcode);

但是，使用C ++ 0x，您将可以写

With C++0x, however, you will be allowed to write

return { "name", zipcode };

且不需要用户定义的构造函数。

and no user-defined constructor is necessary.

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