问题描述
我想为我的标题中的每个类生成唯一的数字，在我的情况下的primes，但让我们说这应该只是连续的数字，1,2,3,4等。
I want to generate unique numbers for each class in my header, primes in my case primes but let's say this should only be consecutive numbers i.e. 1,2,3,4,etc.
当然我可以硬编码这些：
Of course I can hardcode these:
struct A { enum { ID = 1; }; };
struct B { enum { ID = 2; }; };
struct C { enum { ID = 3; }; };
struct D { enum { ID = 4; }; };
这是非常容易出错的，因为在现实中类不是那么小，如果我添加一个新在中间的类如果我不想完全松开ID的概述，我必须更改所有以下数字。
This is very error-prone since in reality the classes are not that small and if I add a new class in the middle I have to change all the following numbers if I don't want to completely loose the overview of the IDs.
我希望我可以做以下：
I wish I could do the following:
struct A { enum { ID = get_next_int(); }; };
struct B { enum { ID = get_next_int(); }; };
struct C { enum { ID = get_next_int(); }; };
struct D { enum { ID = get_next_int(); }; };
但是由于constexpr函数调用不能有副作用afaik，这是不可能的。我认为使用宏这样的结果是不可能的。
But since constexpr functions calls can't have side effects afaik, this is impossible. I think using macros such a result is impossible too.
我也会很幸运的像这样：
I would also be lucky with something like that:
struct A_id_holder : some_base_counter {};
struct A { enum { ID = A_id_holder::ID; }; };
struct B_id_holder : some_base_counter {};
struct B { enum { ID = B_id_holder::ID; }; };
struct C_id_holder : some_base_counter {};
struct C { enum { ID = C_id_holder::ID; }; };
struct D_id_holder : some_base_counter {};
struct D { enum { ID = D_id_holder::ID; }; };
但是老实说，我不知道如何实现。
But honestly, I have no idea how to implement that.
我可以实现我的目标，如果是，如何？
Can I achieve my goal and if yes, how?
推荐答案
c $ c> __ COUNTER __ 宏。但这是非标准的，并且整个程序只有一个。
Most people do this with the __COUNTER__ macro. But that's nonstandard, and there's only one for the whole program.
这里是一个我想出了使用符合标准并支持多个计数器的模板和重载。
Here is a C++ hack I came up with using templates and overloading which is standard-compliant and supports multiple counters.
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