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  1. class Base {
  2. public:
  3.     virtual void func1() = 0;
  4.     virtual void func2() = 0;
  5.  
  6.     virtual ~Base(){}
  7. };
  8.  
  9. #include <iostream>
  10. #include <memory>
  11.  
  12. class Derived : public Base
  13. {
  14.   struct F1Strategy { 
  15.     virtual void f1Impl() = 0; 
  16.     virtual ~F1Strategy() {}
  17.   };
  18.  
  19.   struct Impl1 : F1Strategy {
  20.     void f1Impl() override { std::cout << "one!\n"; }
  21.   };
  22.  
  23.   struct Impl2 : F1Strategy {
  24.     void f1Impl() override { std::cout << "two?\n"; }
  25.   };    
  26.  
  27.   std::unique_ptr<F1Strategy> f1Strategy;
  28. public:
  29.   Derived() 
  30.     : f1Strategy(new Impl1())
  31.   {}
  32.  
  33.   void func1() override { f1Strategy->f1Impl(); }
  34.  
  35.   void func2() override { 
  36.     static std::unique_ptr<F1Strategy> otherStrategy(new Impl2());
  37.     f1Strategy.swap(otherStrategy);
  38.   }
  39. };
  40.  
  41. int main() {
  42.   std::unique_ptr<Base> pb(new Derived());
  43.   pb->func1();  //  ==> one!
  44.   pb->func2();  //swap
  45.   pb->func1();  //  ==> two?
  46.   pb->func1();  //  ==> two?
  47.   pb->func2();  //swap
  48.   pb->func1();  //  ==> one!
  49. }
  50.  
  51.  
Success #stdin #stdout 0s 3032KB
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Standard input is empty
stdout
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one!
two?
two?
one!
https://ideone.com/zk3UTI
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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