使用可变参数模板创建静态数组 [英] Create static array with variadic templates

问题描述

有一个关于stackoverflow的答案（我似乎不再找到了），它演示了如何在C ++ 11中使用可变参数模板在编译时创建一个静态数组：

There was an answer on stackoverflow (which I can't seem to find anymore) which demonstrated how a variadic template can be used in C++11 to create a static array at compile time:

template <class T, T... args> 
struct array_
{
    static const T data[sizeof...(args)];
};

template <class T, T... args> 
const T array_<T, args...>::data[sizeof...(args)] = { args... };

可以提供递归元函数来实例化 array _ 有任何数量的参数，然后将在编译时复制到内部数组。

A recursive meta-function could be provided to instantiate array_ with any number of parameters, which will then be copied at compile time into the internal array. It's a useful way to create meta-functions for generating constant arrays at compile time.

但是，一个问题是它依赖于类模板参数 >以获取填充数组的实际值。这导致一个主要的限制：只有积分常数可以用作值模板参数。所以，你不能使用这种技术来生成自定义类型的数组。

However, one problem is that it depends on class template parameters to get the actual values to populate the array. This results in one major limitation: only integral constants can be used as value template parameters. So, you can't use this technique to generate arrays of custom types.

我试图想办法解决这个限制，但不能想出任何东西。有没有办法让这个技巧与非整数常数一起使用？

I tried to think of something to work around this limitation, but can't come up with anything. Is there any way to make this technique work with non-integral constants?

推荐答案

自定义类型（即类）实例，只要它们可以从整数类型（或任何其他类型可以作为非模板参数提供，这里我不打算枚举）构造。

Well, you can indeed populate a static array with custom types (i.e. classes) instances provided that they are constructable from integer types (or whatever other types one may provide as non template parameters and which I am not going enumerate here).

只需看看下面的例子，我相信这是很清楚自己解释：

Just take look at the example bellow, which I believe is clear enough to be self explaining:

#include <iostream>

template<typename T>
class my_class
{
    public:
        my_class(T)
        {
            //construct
        }

        void print_something()
        {
            std::cout << "something\n";
        }
};

template<class C, class T, T ... args>
struct array_
{
        static C data[sizeof...(args)];
};

template<class C, class T, T ... args>
C array_<C, T, args...>::data[sizeof...(args)] = {C(args)...};

int main()
{
    array_<my_class<int> , int, 1, 200, 0, 42>::data[2].print_something();
}

注意：在GCC 4.6下编译得很好

Note: compiled just fine under GCC 4.6

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