结合使用带模板类和显式实例化模板的pimpl

问题描述

当我显式实例化模板时，如何将pimpl用于模板化类?

How do I use pimpl for a templated class, when I explicitly instantiate the templates?

我只需要一个示例代码.

All I need is an example code.

我尝试过的是:

// MyTemplatedClass.h

template< class T >
class MyTemplatedClass
{
private:
    class Impl;
    Impl* _pimpl;

public:
    void PublicMethod();
}

我的实现在这里:

// MyTemplatedClass.cpp

template< class T >
class MyTemplatedClass<T>::Impl
{
    public:
        void PublicMethod();
}

template <class T>
void MyTemplatedClass<T>::Impl::PublicMethod()
{
    ...
}

对实现类的转发方法调用:

Forwarding method call to implementation class:

template< class T >
void MyTemplatedClass<T>::PublicMethod()
{
    _pimpl->PublicMethod();
}

显式实例化:带有int和double的示例:

Explicit instantiation:Example with int and double:

template class MyTemplatedClass< int >;
template class MyTemplatedClass< double >;

但这似乎不起作用.

推荐答案

这将回答您的问题，但是我怀疑它是否可以实现您希望实现的目标.我怀疑您可能想在MyTemplatedClass范围之外声明模板实现.从模板实现继承而不是将其作为成员变量可能是一个更好的设计.

This would answer your question, but I doubt it does what you hoped to achieve. I suspect you would want to declare the template implementation outside the scope of MyTemplatedClass. It might be a better design to inherit from the template implementation instead of having it as a member variable.

如果您的编译器不支持外部模板声明，则无法看到具有指向实现的模板指针会增加任何值.毕竟，您还是必须将要隐藏的实现详细信息隐藏在头文件中.

If you compiler does not support extern template declarations I cannot see that having a template pointer to implementation adds any value. You would after all have to have the implementation details you wanted to hide away in the header file anyway.

#include <iostream>

template < class T > class MyTemplatedClass {
private:
  template < class U> class Impl {
  public:
     void ImplPublicMethod() {
           std::cout << "Standard implementation" << std::endl;
           }
  };

  Impl<T> * _pimpl;
public:
  MyTemplatedClass() : _pimpl(new Impl<T>) { }
  ~MyTemplatedClass() { delete _pimpl; }
  void publicMethod() {
     _pimpl->ImplPublicMethod();
  }
};

template<> class MyTemplatedClass<int> {
private:
  class Impl {
  public:
     void ImplPublicMethod() {
          std::cout << "Integer specialisation" << std::endl;
     };
 };

 Impl * _pimpl;
public:
  MyTemplatedClass() : _pimpl(new Impl) { }
  ~MyTemplatedClass() { delete _pimpl; }
  void publicMethod() {
     _pimpl->ImplPublicMethod();
  }
};

int main(int argc, char ** argv) {

   MyTemplatedClass<char> charVersion;
   charVersion.publicMethod();

   MyTemplatedClass<int> intVersion;
   intVersion.publicMethod();

   return 0;
}

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