Detecting array type do not works.

Question

template<typename T> 
class CompoundT {           // primary template 
  public: 
    enum { IsPtrT = 0, IsRefT = 0, IsArrayT = 0, 
           IsFuncT = 0, IsPtrMemT = 0 }; 
    typedef T BaseT; 
    typedef T BottomT; 
    typedef CompoundT<void> ClassT; 
};

template<typename T, size_t N> 
class CompoundT <T[N]> {    // partial specialization for arrays 
  public: 
    enum { IsPtrT = 0, IsRefT = 0, IsArrayT = 1, 
           IsFuncT = 0, IsPtrMemT = 0 }; 
    typedef T BaseT; 
    typedef typename CompoundT<T>::BottomT BottomT; 
    typedef CompoundT<void> ClassT; 
}; 

and in main:

template<class T>
bool isArray(T a)
{
    return CompoundT<T>::IsArrayT;
}

int _tmain(int argc, _TCHAR* argv[])
    {
        int a[10];
        cout << isArray(a);
        return 0;
}

Why this doesn't work? This example is from "Templates the complete guide" ch.19.2.

Answer 1

Because isArray must take reference, otherwise if you take an array by value it's the same as if you take a pointer :)

template <class T>
bool isArray(const T& ) {...}

because

void f(int a[10]);

and

void f(int* a);

are equivalent declarations.