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  1. #include <iostream>
  2. #include <initializer_list>
  3. #include <array>
  4. #include <tuple>
  5.  
  6. template<typename T, std::size_t N>
  7. struct ArrayInitializer {
  8.     template<typename U> struct id { using type = U; };
  9.     std::array<T, N> t;
  10.  
  11.     template<typename U = std::initializer_list<T>>
  12.     ArrayInitializer(typename id<U>::type z) 
  13.         :ArrayInitializer(z, std::make_index_sequence<N>())
  14.     { 
  15.         if(N > z.size())
  16.             throw std::out_of_range("that's crazy!");
  17.     }
  18.  
  19.     template<typename ...U>
  20.     ArrayInitializer(U &&... u)
  21.        :t{ std::forward<U>(u)... }
  22.     { }
  23.  
  24. private:
  25.     template<std::size_t ...Ns>
  26.     ArrayInitializer(std::initializer_list<T>& t,
  27.                      std::index_sequence<Ns...>)
  28.        :t{ *(t.begin() + Ns) ... }
  29.     { }
  30. };
  31.  
  32. template<typename T, std::size_t N>
  33. std::array<T, N> f(ArrayInitializer<T, N> ai) {
  34.     return std::move(ai.t);
  35. }
  36.  
  37. int main() {
  38.    f<int, 5>({1, 2, 3, 4, 5});  // OK 
  39.    //f<int, 5>({1, 2, 3, 4, 5, 6});  // error - "too many initializers for array<int, 5>"
  40.  
  41.    std::initializer_list<int> il{1, 2, 3, 4, 5};
  42.    f<int, 5>(il); // ok
  43. }
Success #stdin #stdout 0s 3452KB
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https://ideone.com/fbnM6W
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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