C++:非临时常量引用

问题描述

我需要编写一个类，其构造函数接受一个对象的常量引用并将其存储在本地.

I need to write a class whose constructor takes a constant reference to a object and stores it locally.

为了避免我能预见的最常见的错误，我只想接受对非临时的引用(即:对左值的引用).

In order to avoid most common mistakes I can foresee, I'd like to only accept references to non-temporary (ie: references to lvalues).

如何编写一个只对非临时对象进行常量引用的函数?

How can I write a function that takes constant references to non-temporary only?

当然，即使是非临时的也可能超出范围，从而破坏我的类行为，但我相信通过禁止临时引用，我将避免大多数错误.

Of course even a non-temporary could go out of scope and thus break my class behavior, but I believe that by disallowing temporary references I will avoid most mistakes.

推荐答案

如果你要存储一个引用并且需要在构造函数完成后使用它，那么构造函数最好带一个指针:

If you are going to store a reference and need to use it after the constructor has completed, it's probably best for the constructor to take a pointer:

struct C {
    C(const X* p) : p_(p) { }

    const X* p_;
};

这样，几乎可以保证你不会有一个指向临时的指针(除非 X 做了一些非常愚蠢的事情，比如重载一元 & 到返回this).

This way, it's pretty much guaranteed that you won't have a pointer to a temporary (unless X does something really dumb, like overloading the unary & to return this).

如果构造函数接受一个指针，类的用户也更清楚他们需要注意他们传递给构造函数的 X 对象的生命周期.

If the constructor takes a pointer, it's also clearer to users of the class that they need to pay attention to the lifetime of the X object they pass to the constructor.

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