CPP模板成员函数专门化 [英] CPP templated member function specialization

问题描述

 模板< ; class Derived，class T> 
 class AbstractWavelet {
 public：
 [...] 
 
 template< bool useCache> 
 const typename T :: scalar moment（const int i，const int j）const {
 return abstractWaveletSpecialization< Derived，T，useCache> :: moment（static_cast< const Derived *> i，j）; 
} 
 template< bool useCache> 
 friend const typename T :: scalar abstractWaveletSpecialization< Derived，T，useCache> :: moment（const Derived * const，const int i，const int j）; 
 
 protected：
 //返回第i个缩放函数的第j个时刻
 template< bool useCache> 
 inline const typename T :: scalar momentImpl（const int j，const int i）const {
 [...] 
} // momentImpl 
} 
  

实际的专门化发生在额外的abstractWaveletSpecialization结构中：

 模板< class Derived，class T，bool useCache> 
 struct abstractWaveletSpecialization {
 inline static const typename T :: scalar moment（const Derived * const，const int i，const int j）{
 return that-> momentImpl< useCache> i，j）; 
} 
}; 
 
 
 template< class Derived，class T> 
 struct abstractWaveletSpecialization< Derived，T，true> {
 
 typedef const std :: pair< const int，const int> momentCacheKey; 
 typedef std :: map< momentCacheKey，
 const typename T :: scalar> momentCacheType; 
 static momentCacheType momentCache; 
 
 
 inline static const typename T :: scalar moment（const Derived * const，const int i，const int j）{
 momentCacheKey cacheKey（i，j）; 
 typename momentCacheType :: iterator idx = momentCache.find（cacheKey）; 
 
 if（idx == momentCache.end（））
 return that-> momentImpl< true>（i，j）; // COMPILE ERROR HERE 
 else 
 return momentCache [cacheKey]; 
} 
};问题是我不能在专门的abstractWaveletSpecialization结构中调用momentImpl（）：
 $ 
 b 
 $ b 
 错误：无效的操作数类型'<未解析的重载函数类型>'和'bool'二进制操作符<'
  
但编译器不会在非专门的abstractWaveletSpecialization结构中调用momentImpl。
 
 
 
我的方法在C ++中被禁止了吗？ 
解决方案
你可以尝试 that-> template momentImpl< ; true>（i，j）; 请问？ 
这是一种告诉编译器嘿，后面的事情 - >是一个模板调用的方式。
 
I'm trying to specialize the member function moment() only (not the hole class) like this:
template<class Derived, class T>
class AbstractWavelet {
public:
  [...]

  template<bool useCache>
  const typename T::scalar moment(const int i, const int j) const {
    return abstractWaveletSpecialization<Derived, T, useCache>::moment(static_cast<const Derived*>(this), i, j);
  }
  template<bool useCache>
  friend const typename T::scalar abstractWaveletSpecialization<Derived, T, useCache>::moment(const Derived* const that, const int i, const int j);

protected:
  // returns the jth moment of the ith scaling function
  template<bool useCache>
  inline const typename T::scalar momentImpl(const int j, const int i) const {
    [...]
  } // momentImpl
};
The actual specialization happens in an extra abstractWaveletSpecialization struct:
template<class Derived, class T, bool useCache>
struct abstractWaveletSpecialization {
  inline static const typename T::scalar moment(const Derived* const that, const int i, const int j) {
    return that->momentImpl<useCache>(i,j);
  }
};


template<class Derived, class T> 
struct abstractWaveletSpecialization<Derived, T, true> {

  typedef const std::pair<const int, const int> momentCacheKey;
  typedef std::map<momentCacheKey,
               const typename T::scalar> momentCacheType;
  static momentCacheType momentCache;


  inline static const typename T::scalar moment(const Derived* const that, const int i, const int j) {
    momentCacheKey cacheKey(i,j);
    typename momentCacheType::iterator idx = momentCache.find(cacheKey);

    if (idx == momentCache.end())
      return that->momentImpl<true>(i, j);  // COMPILE ERROR HERE
    else
      return momentCache[cacheKey];
  }
};
The problem is that I cannot call momentImpl() in the specialized abstractWaveletSpecialization struct:
error: invalid operands of types ‘<unresolved overloaded function type>’ and ‘bool’ to binary ‘operator<’
But the compiler does not complain about the call of momentImpl in the non-specialized abstractWaveletSpecialization struct.

Is my approach forbidden in C++? Or is there any way to make this work?
解决方案
Can you try that->template momentImpl<true>(i, j); please ?
It's a way to tell the compiler "Hey, the thing after -> is a templated call"

                        
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