是否有可能有一个“自动"?成员变量? [英] Is it possible to have an "auto" member variable?

问题描述

例如，我想要一个 auto 类型的变量，因为我不确定它是什么类型.

当我尝试在类/结构声明中声明它时，它给了我这个错误:

<块引用>

无法推断自动类型.需要初始化程序

有办法解决吗?

struct Timer {自动开启;};

解决方案

可以，但是必须声明static和const:

struct Timer {静态常量自动启动 = 0;};

Coliru 中的一个工作示例.

由于此限制，您不能将 start 作为非静态成员，并且不能在不同的对象中具有不同的值.

如果你想为不同的对象使用不同类型的start，最好将你的类作为模板

template结构定时器{开始；};

如果你想推导T的类型，你可以制作一个类似工厂的函数来进行类型推导.

template定时器::type>MakeTimer(T&& startVal) {//转发参数return Timer::type>{std::forward(startVal)};}

实例.

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

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

Cannot deduce auto type. Initializer required

Is there a way around it?

struct Timer {

    auto start;

};

解决方案

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

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

A working example in Coliru.

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

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

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

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)};
}

Live example.

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