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  1. #include <functional>
  2.  
  3. template<typename Number,
  4.          typename AdvanceOperation = std::plus<Number>>
  5. class sequence_generator
  6. {
  7.   public:
  8.     sequence_generator(Number start_value = Number{},
  9.                                  Number step_size = Number{1},
  10.                                  AdvanceOperation advancer = AdvanceOperation{})
  11.                                  : current_value{start_value},
  12.                                    step_size{step_size},
  13.                                    advancer{advancer}
  14.     {}
  15.  
  16.     auto operator()()
  17.     {
  18.       return next();
  19.     }
  20.  
  21.     auto next()
  22.     {
  23.       auto tmp = current_value;
  24.       current_value = advancer(current_value, step_size);
  25.       return tmp;
  26.     }
  27.   private:
  28.     Number current_value;
  29.     Number step_size;
  30.     AdvanceOperation advancer;
  31. };
  32.  
  33. template<typename Number, typename AdvanceOperation=std::plus<Number>>
  34. auto make_sequence_generator(Number start_value, Number step_size,
  35.                              AdvanceOperation advancer)
  36. {
  37.     return sequence_generator<Number, AdvanceOperation>{start_value, step_size,
  38.                                                         advancer};
  39. }
  40.  
  41. #include <algorithm>
  42. #include <iostream>
  43. #include <vector>
  44. #include <cassert>
  45.  
  46. int main()
  47. {
  48.   std::vector<int> vector(10);
  49.   std::generate(std::begin(vector), std::end(vector),
  50.                 sequence_generator<int>{});
  51.   assert(vector == std::vector<int>({0,1,2,3,4,5,6,7,8,9}));
  52.   std::generate(std::begin(vector), std::end(vector),
  53.                 make_sequence_generator(1,2,std::multiplies<>{}));
  54.   assert(vector == std::vector<int>({1,2,4,8,16,32,64,128,256,512}));
  55. }
Success #stdin #stdout 0s 3408KB
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https://ideone.com/Zjgpr6
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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