template argument involves template parameter(s)

A partially specialized non-type argument expression shall not involve a template parameter of the partial specialization except when the argument expression is a simple identifier.




template<typename T> struct DefOpt{
  static const int value=0;
};


template<typename T> struct DefClass{
  typedef T DefT;
};




template<typename T,typename V=typename DefClass<T>::DefT,int val=DefOpt<T>::value> 
struct DefAccPol{
};




template<typename T>
struct A{
};




template<>
struct DefAccPol< int >{
};




template<typename T>
struct DefAccPol< A<T> >{
};




int main(){
  DefAccPol<A<int> > at;


}


===compiler output===

error: template argument ‘DefOpt<A<T> >::value’ involves template parameter(s)

the reason int val=DefOpt<T>::value

the type (DefClass<T>::DefT) is fine.

template<>

struct DefAccPol< int >{

}; 

is fine as well, because it has no templates 

only the combination of int val=.. and template<typename T> partial specialization is bad

similarly


template<typename T>
struct DefAccPol< A<T>,T,DefOpt<T>::value >{
};


is not accepted, but


template<typename T>
struct DefAccPol< A<T>,T,0 >{
};

is ok