c++ - Compile time checking for the number of arguments in a variadic template -

i made generic n-dimensional array class, want make safer compile-time checks.

the constructor , operator() expected work correctly when number of arguments given equals dimension. still, if write code like

array<int, 2> a(1, 2, 3); //3 dimensions 2d array == crash 

or

array<int> a(1); //plain 1d array std::cout << a(1, 2); //segfault 

it silently compiles, , need run debugger, it's quite confusing debug variadic templates.

can think of way provide compile time check correct number of arguments matching dimension?

template<typename t, int dimension = 1> class array { private:     std::unique_ptr<t[]> pointer;     int size[dimension];     int realsize;  public:     array()     {     }      template<typename... ns>     array(ns... ns)     : realsize(1)     {         create(1, ns...);     }  private:     template<typename... ns>     void create(int d, int n, ns... ns)     {         realsize *= n;         size[d - 1] = n;         create(d + 1, ns...);     }      void create(int d)     {         pointer = std::unique_ptr<t[]>(new t[realsize]);     }      int computesubsize(int d) const     {         if (d == dimension)         {             return 1;         }         return size[d] * computesubsize(d + 1);     }      template<typename... ns>     int getindex(int d, int n, ns... ns) const     {         return n * computesubsize(d) + getindex(d + 1, ns...);     }      int getindex(int d) const     {         return 0;     }  public:     template<typename... ns>     t& operator()(ns... ns) const     {         return pointer[getindex(1, ns...)];     }      int getsize(int d = 1) const     {         return size[d - 1];     } }; 

you can add compile time assert statements @ right places prevent code like

array<int, 2> a1(1, 2, 3); 

and

array<int> a3(1); std::cout << a3(1, 2); 

from being compiled.

here's once place:

  template<typename... ns>      array(ns... ns)      : realsize(1)      {         static_assert(sizeof ...(ns) == dimension, "incorrect number of arguments");         create(1, ns...);      } 

that prevents line

array<int, 2> a1(1, 2, 3); 

from being compiled.

another place:

  template<typename... ns>      t& operator()(ns... ns) const      {         static_assert(sizeof ...(ns) == dimension, "incorrect number of arguments");         return pointer[getindex(1, ns...)];      } 

that prevents

array<int> a3(1); std::cout << a3(1, 2); 

from being compiled.

here valid statements:

array<int, 2> a2(1, 2);  array<int> a3(1); std::cout << a3(0);