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  1. #include <array>
  2. #include <type_traits>
  3.  
  4. template<int ...N>
  5. struct valuelist : std::integral_constant<int, sizeof...(N)> {} ;
  6.  
  7. //usage: generate_valuelist<5>::type gives valuelist<0,1,2,3,4>
  8. template<int N>
  9. class generate_valuelist
  10. {
  11.     template<int I, int ...Is>
  12.     struct gen : gen<I-1, I-1, Is...> {};
  13.  
  14.     template<int ...Is>
  15.     struct gen<0, Is...> { typedef valuelist<Is...> type; };
  16.  public:
  17.     typedef typename gen<N>::type type;
  18. };
  19.  
  20. template<typename T, int...args>
  21. auto repeat(T value, valuelist<args...>) -> std::array<T, sizeof...(args)> 
  22. {
  23.    //unpack args, repeating `value` sizeof...(args) times
  24.    //note that (X, value) evaluates to value
  25.    return {(args, value)...}; 
  26. }
  27.  
  28. struct A{
  29.   A(int){}  
  30. };
  31.  
  32.  
  33. template<typename T, size_t N>
  34. std::array<T, N>
  35. filled_array(T const& u)
  36. {
  37.     //generate_valuelist<N>::type gives valuelist<0,1,...N-1>
  38.     typename generate_valuelist<N>::type pack;
  39.     std::array<T, N> items = repeat(u, pack);
  40.     return items;
  41. }
  42.  
  43. int main() {
  44.     auto x = filled_array<A, 5>(A(1));
  45. }
Success #stdin #stdout 0s 3336KB
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https://ideone.com/UFadRE
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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