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  1. #include <vector>
  2. #include <iostream>
  3. #include <iterator>
  4. #include <array>
  5. using namespace std;
  6.  
  7. class Generator {
  8. protected:
  9.     vector<int> v;
  10. public:
  11.     Generator(unsigned length): v(length) {}
  12.  
  13.     template<class Outputter>
  14.     void do_calculations_with_output(Outputter& out){
  15.         // perform first part of some complex operations on v
  16.         out.output(v);
  17.         // perform second part of some complex operations on v
  18.         out.output(v);
  19.         // perform some final actions
  20.     }
  21.  
  22. };
  23.  
  24. class SimpleDumpOutputter {
  25. private:
  26.  
  27.     ostream* out;
  28.     unsigned count;
  29. public:
  30.     SimpleDumpOutputter(ostream& os): out(&os), count() {}
  31.     template<class C>
  32.     void output(const C& c) {
  33.         *out << "Step " << ++count << " of calculation: ";
  34.         copy(c.begin(),c.end(), ostream_iterator<int>(*out, " "));
  35.         *out << endl;
  36.     }
  37. };
  38.  
  39. class FancyOutputter {
  40.     ostream* out;
  41.     int count;
  42. public:
  43.     FancyOutputter(ostream& os): out(&os),count() {}
  44.     template<class C>
  45.     void output(const C& c) {
  46.         // create a graph using graphviz's dot language to ease visualisation of v
  47.         *out << "Step " << ++count << " of calculation: ";
  48.        *out << "Graphviz output\n";
  49.     }
  50. };
  51.  
  52. template<class... Outputters> class AggregateOutputter : private Outputters... {
  53. private:
  54.    template<class First, class... Rest>
  55.    struct output_helper{
  56.       template<class C>
  57.       static void do_output(AggregateOutputter* pthis,const C& c){
  58.           static_cast<First*>(pthis)->output(c);
  59.           output_helper<Rest...>::do_output(pthis,c);
  60.       }
  61.  
  62.    };
  63.  
  64.    template<class First>
  65.    struct output_helper<First>{
  66.       template<class C>
  67.       static void do_output(AggregateOutputter* pthis,const C& c){
  68.           static_cast<First*>(pthis)->output(c);
  69.       }
  70.  
  71.    };
  72. public:
  73.    template<class... Out>
  74.     AggregateOutputter( Out&... out): Outputters(out)...{}
  75.     template<class C>
  76.     void output(const C& c) {
  77.         output_helper<Outputters...>::do_output(this,c);
  78.     }
  79.  // first argument is dummy, because we would use the ostreams in destinations
  80. };
  81. int main(){
  82.  
  83. AggregateOutputter<FancyOutputter,SimpleDumpOutputter> out(cout,cout);
  84.  
  85. Generator g(10);
  86.  
  87. g.do_calculations_with_output(out);
  88.  
  89. }
Success #stdin #stdout 0s 2984KB
comments (?)
stdin 
Standard input is empty
stdout 
Step 1 of calculation: Graphviz output
Step 1 of calculation: 0 0 0 0 0 0 0 0 0 0 
Step 2 of calculation: Graphviz output
Step 2 of calculation: 0 0 0 0 0 0 0 0 0 0
https://ideone.com/xQrnW4
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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