模板元编程转换类型为唯一编号 [英] Template metaprogram converting type to unique number
问题描述
我刚刚开始使用元编程,我正在开发不同的任务只是为了探索领域。其中之一是生成唯一的整数并将其映射到类型,如下所示:
I just started playing with metaprogramming and I am working on different tasks just to explore the domain. One of these was to generate a unique integer and map it to type, like below:
int myInt = TypeInt<AClass>::value;
其中值应为编译时常数,这可以在元程序中进一步使用。
Where value should be a compile time constant, which in turn may be used further in meta programs.
我想知道这是否可能,在这种情况下如何。因为虽然我已经学习了很多关于探索这个主题,我仍然没有得出一个答案。
I want to know if this is at all possible, and in that case how. Because although I have learned much about exploring this subject I still have failed to come up with an answer.
(PS A是/否的答案比C ++更令人满意解决方案,不使用元编程,因为这是我正在探索的域)
(P.S. A yes/no answer is much more gratifying than a c++ solution that doesn't use metaprogramming, as this is the domain that I am exploring)
推荐答案
far能够保持一个类型的列表,同时跟踪到基地的距离(给出一个唯一的值)。注意,如果你正确地跟踪事物,那么这里的位置将是唯一的(参见示例的主要)。
The closest I've come so far is being able to keep a list of types while tracking the distance back to the base (giving a unique value). Note the "position" here will be unique to your type if you track things correctly (see the main for the example)
template <class Prev, class This>
class TypeList
{
public:
enum
{
position = (Prev::position) + 1,
};
};
template <>
class TypeList<void, void>
{
public:
enum
{
position = 0,
};
};
#include <iostream>
int main()
{
typedef TypeList< void, void> base; // base
typedef TypeList< base, double> t2; // position is unique id for double
typedef TypeList< t2, char > t3; // position is unique id for char
std::cout << "T1 Posn: " << base::position << std::endl;
std::cout << "T2 Posn: " << t2::position << std::endl;
std::cout << "T3 Posn: " << t3::position << std::endl;
}
这样做很自然,以某种方式指定prev类型。最好找出一种自动跟踪这种方法。也许我会玩它一些,看看是否可能。绝对是一个有趣/有趣的谜题。
This works, but naturally I'd like to not have to specify a "prev" type somehow. Preferably figuring out a way to track this automatically. Maybe I'll play with it some more to see if it's possible. Definitely an interesting/fun puzzle.
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