c – 没有调用复制构造函数,但编译器抱怨没有

#include <boost/noncopyable.hpp>

enum Error { ERR_OK=0 };

struct Filter : private boost::noncopyable
{
  Filter() {}
  virtual ~Filter() {}

  virtual int filter(int* data) const = 0;

};

struct  SpecialFilter : public Filter,private boost::noncopyable
{
  inline SpecialFilter(unsigned int min,unsigned int max) : min(min),max(max) {}
  virtual ~SpecialFilter() {}

  virtual int filter(int* data) const
  {
    // ...
    return ERR_OK;
  }

  unsigned int min;
  unsigned int max;
};

struct AClass
{
  AClass() {}
  AClass(const AClass& other) {}
  ~AClass() {}

  int specialFilter(int channel,int minThreshold,int maxThreshold)
  {
    // ...
    return filter(channel,SpecialFilter(123,321));
  }

  int filter(int channel,const Filter& filter)
  {
    // ...
    return ERR_OK;
  }

};

我的编译器(GCC 4.2)抱怨：

- warning: direct base ‘boost::noncopyable_::noncopyable’ inaccessible in ‘SpecialFilter’ due to ambiguity
- noncopyable.hpp: In copy constructor ‘Filter::Filter(const Filter&)’:
- noncopyable.hpp:27: error: ‘boost::noncopyable_::noncopyable::noncopyable(const boost::noncopyable_::noncopyable&)’ is private
- synthezised method first required here: [return filter(channel,321));]

但是我没有调用复制构造函数！