C ++构造，其行为类似于__COUNTER__宏 [英] C++ construct that behaves like the __COUNTER__ macro

问题描述

我有一组C ++类，每个都必须声明一个唯一的顺序ID作为编译时常量。
为此，我使用 __ COUNTER __ 内置宏，它转换为一个整数，每次出现时递增。 ids不需要遵循严格的顺序。唯一的要求是它们是顺序的，从0开始：

I have a set of C++ classes and each one must declare a unique sequential id as a compile-time constant. For that I'm using the __COUNTER__ built-in macro which translates to an integer that is incremented for every occurrence of it. The ids need not to follow a strict order. The only requirement is that they are sequential and start from 0:

class A {
public:
    enum { id = __COUNTER__ };
};

class B {
public:
    enum { id = __COUNTER__ };
};

// etcetera ...

我的问题是：使用C ++结构（例如模板）可以实现相同的结果？

My question is: Is there a way to achieve the same result using a C++ construct, such as templates?

推荐答案

code> __ LINE __ 宏和模板：

Here is a possible way to do it using __LINE__ macro and templates:

template <int>
struct Inc
{
    enum { value = 0 };
};

template <int index>
struct Id
{
    enum { value = Id<index - 1>::value + Inc<index - 1>::value };
};

template <>
struct Id<0>
{
    enum { value = 0 };
};

#define CLASS_DECLARATION(Class) \
template <> \
struct Inc<__LINE__> \
{ \
    enum { value = 1 }; \
}; \
 \
struct Class \
{ \
    enum { id = Id<__LINE__>::value }; \
private:

使用示例：

CLASS_DECLARATION(A)
    // ...
};

CLASS_DECLARATION(B)
    // ...
};

CLASS_DECLARATION(C)
    // ...
};

请参阅实例。

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