如何计算模板类的CRTP子类的数量？ [英] How to count the number of CRTP subclasses of a template class?

问题描述

有没有人知道使用CRTP来计算对象子类数量的方法？

Does anyone know of a method to use CRTP to count the number of subclasses of an object?

假设我们的设置类似于下面的一个： p>

Suppose we had a setup similar to the following one:

template <typename T>    
class Object
{
    ....  
};

const unsigned int ObjectSubClassCount = ...; 

class Subobject : public Object<SubObject>
{
    ....
};

class Second : public Object<Second>
{
    ....
};

等等，使用TMP，我们可能有一个常数> ObjectSubClassCount ）表示子类的总数？

and so on, such that, using TMP, we might have a constant (ObjectSubClassCount) that represents the total number of subclasses?

有没有人知道这样做的方法？

Does anyone know a way to do this?

编辑：我想以后使用结果作为模板参数，所以我需要它完成与TMP ...

I am wanting to use the result as a template parameter later on, so I need it to be done with TMP...

推荐答案

不需要使用结果作为模板参数，我会尝试这样做：

Without the requirement to use the result as a template parameter later I would try it doing like this:

// Class which increments a given counter at instanciation
struct Increment {
  Increment(std::size_t& counter)
  {
    counter++;
  }
};

// This is your template base
template <typename T>    
class Object
{
  private:
    // For every instanciation of the template (which is done for a subclass)
    // the class counter should get incremented
    static Increment incrementCounter;
};

// This is the global object counter
static std::size_t classCounter;

// Static Member Variable
template<typename T>
Object<T>::incrementCounter(classCounter);

尚未尝试，但应该这样做。要使结果再次作为模板参数（MPL），我没有足够的MPL经验，但我怀疑这是可能的。

Haven't tried it but should do. To have the result available as a template parameter again (MPL) I don't have enough experience in MPL but I doubt this is possible.

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