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  1. #include <future>
  2. #include <memory>
  3. #include <iostream>
  4.  
  5. class IWidget {
  6. public:
  7.   virtual ~IWidget(){}
  8.   virtual std::future<double> calculateSomethingAsync() const = 0;
  9. };
  10.  
  11. class Widget : public std::enable_shared_from_this<Widget>, public IWidget {
  12.   double data;
  13.  
  14.   double calculateSomethingInternal() const;
  15. protected:
  16.   Widget(double init) : data(init) {}  // protected, use create
  17. public:
  18.   std::future<double> calculateSomethingAsync() const override;
  19.  
  20.   static std::shared_ptr<IWidget> create(double init);
  21. };
  22.  
  23. std::shared_ptr<IWidget>
  24. Widget::create(double init) {
  25.   return std::shared_ptr<IWidget>(new Widget(init));
  26. }
  27.  
  28. double
  29. Widget::calculateSomethingInternal() const {
  30.   return (data + 5.0) / 2.0;
  31. }
  32.  
  33. std::future<double>
  34. Widget::calculateSomethingAsync() const {
  35.   auto shared_this = shared_from_this();
  36.   return std::async([shared_this]{ return shared_this->calculateSomethingInternal(); });
  37. }
  38.  
  39. int main() {
  40.     std::future<double> result_task;
  41.     {
  42.       std::shared_ptr<IWidget> w = Widget::create(42.0);  
  43.       result_task = w->calculateSomethingAsync();
  44.     }  // w shared_ptr goes out-of-scope here.
  45.     auto result = result_task.get();
  46.     std::cout << result << "\n";
  47. }
Success #stdin #stdout 0s 3472KB
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23.5
https://ideone.com/DIxSAv
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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