是否有可能具有“自动"功能?成员变量? [英] Is it possible to have an "auto" member variable?

问题描述

例如，我想拥有类型为auto的变量，因为我不确定它将是哪种类型.

For example I wanted to have a variable of type auto because I'm not sure what type it will be.

当我尝试在类/结构声明中声明它时，出现此错误:

When I try to declare it in class/struct declaration it's giving me this error:

无法推断自动类型.需要初始化器

Cannot deduce auto type. Initializer required

有办法解决吗?

struct Timer {

    auto start;

};

推荐答案

可以，但是必须声明static和const:

You can, but you have to declare it static and const:

struct Timer {
    static const auto start = 0;
};

Coliru中的工作示例.

因此，使用此限制，您不能将start作为非静态成员，并且在不同的对象中不能具有不同的值.

With this limitation, you therefore cannot have start as a non-static member, and cannot have different values in different objects.

如果要为不同的对象使用不同类型的start，最好将类作为模板

If you want different types of start for different objects, better have your class as a template

template<typename T>
struct Timer {
    T start;
};

如果要推导T的类型，则可以制作一个类似于工厂的函数来进行类型推导.

If you want to deduce the type of T, you can make a factory-like function that does the type deduction.

template<typename T>
Timer<typename std::decay<T>::type> MakeTimer(T&& startVal) {   // Forwards the parameter
   return Timer<typename std::decay<T>::type>{std::forward<T>(startVal)};
}

在线示例.

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