用constexpr std :: string_view枚举vs用std :: string实例化的枚举 [英] Enum with constexpr std::string_view vs instantiated enum with std::string

问题描述

我想让结构持有枚举 s进行迭代，以及 std :: string 保留其名称以创建菜单项。我使用的是这样的东西：

I would like to have structs holding enums for iteration, together with std::string holding their names for creating menu entries. I was using something like this:

struct S
{
    enum E { ONE, TWO, ALL };
    std::array<std::string, ALL> names { "one", "two" };
};
int main()
{
    S s;
    for(int i=s.ONE; i<s.ALL; ++i) // or S::...
        std::cout << s.names[i] << '\n';
    return 0;
}

据我了解，这比拥有全局变量更可取。它可以工作，但是在使用前需要实例化。现在，我发现了这种方法，它需要-std = C ++ 17 进行编译：

As I understand, this is preferred to having global variables. It works, but needs instantiation before usage. Now, I found out about this method, which needs --std=C++17 to compile:

struct S
{
    enum E { ONE, TWO, ALL };
    static constexpr std::array<std::string_view, ALL> names { "one, "two" };
};
int main()
{
    for(int i=S::ONE; i<S::ALL, ++i)
        std::cout << S::names[i] << '\n';
return 0;
}

但是，在内存使用方面，与我以前的方式相比，它的表现如何？怎么做呢？会有什么更好的方法？

But how will this behave, in terms of memory usage, compared to my previous way of doing this? Or is there a wrong way in how I do it? What would be a better way?

推荐答案

您不需要枚举，当使用 std :: array 时，您可以这样做：

You don't need that enum when using std::array. You can do this:

struct S
{
    static constexpr std::array<std::string_view, 2> names { "one", "two" };
};

int main()
{
    for(auto name: S::names)
        std::cout << name << '\n';
}

或者这个：

int main()
{
    for(auto n = std::begin(S::names); n != std::end(S::names); ++n)
        std::cout << *n << '\n';
}

这与您的第一个示例有很大不同，因为现在您只有一个数组用于 每个 S Sruct S 。以前，每个结构都有自己的数组副本。

This is very different from your first example though because now you only have one array for every sruct S. Before, every struct has its own copy of the array.

做适合自己需要的事情。每个对象一个数组？还是一个所有对象的数组？

So do what suits your need. One array per object? Or one array for all your objects?

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