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  1. #include <iostream>
  2. #include <vector>
  3. #include <memory>
  4.  
  5. struct PBaseVisitor;
  6.  
  7. struct PBase {
  8.   virtual int get_id() { return 0; }
  9.   virtual void accept(PBaseVisitor &v);
  10. };
  11. struct P1 : PBase {
  12.   int get_id() override { return 1; }
  13.   void accept(PBaseVisitor &v) override;
  14. };
  15. struct P2 : PBase {
  16.   int get_id() override { return 2; }
  17.   void accept(PBaseVisitor &v) override;
  18. };
  19.  
  20. class SBase {
  21. public:
  22.   virtual ~SBase() {}
  23.   void doIt(PBase &p) { this->internalDoIt(p); }
  24.  
  25. private:
  26.   virtual void internalDoIt(PBase &p) = 0;
  27. };
  28.  
  29. struct PBaseVisitor {
  30.   virtual ~PBaseVisitor() {}
  31.   virtual void visit(PBase &p) = 0;
  32.   virtual void visit(P1 &p) { visit(static_cast<PBase &>(p)); };
  33.   virtual void visit(P2 &p) { visit(static_cast<PBase &>(p)); };
  34. };
  35.  
  36. void PBase::accept(PBaseVisitor &v) { v.visit(*this); }
  37. void P1::accept(PBaseVisitor &v)    { v.visit(*this); }
  38. void P2::accept(PBaseVisitor &v)    { v.visit(*this); }
  39.  
  40. class S : public SBase {
  41.   struct doItImpl : PBaseVisitor {
  42.     doItImpl(S *s) : s(s) {}
  43.     S *s;
  44.     virtual void visit(PBase &p) { s->internalDoItImpl(p); };
  45.     void visit(P1 &p) override   { s->internalDoItImpl(p); };
  46.     void visit(P2 &p) override   { s->internalDoItImpl(p); };
  47.   };
  48.   virtual void internalDoIt(PBase &p) {
  49.     doItImpl impl(this);
  50.     p.accept(impl);
  51.   }
  52.   void internalDoItImpl(PBase &p) { std::cout << "PBase: " << p.get_id() << '\n'; }
  53.   void internalDoItImpl(P1 &p)    { std::cout << "P1: " << p.get_id() << '\n'; }
  54.   void internalDoItImpl(P2 &p)    { std::cout << "P2: " << p.get_id() << '\n'; }
  55. };
  56.  
  57. int main() {
  58.   std::vector<std::unique_ptr<PBase> > vec;
  59.   vec.emplace_back(new PBase);
  60.   vec.emplace_back(new P1);
  61.   vec.emplace_back(new P2);
  62.  
  63.   S s;
  64.   SBase &bref = s; // Angenommn, dass du von irgendwo her einen
  65.                    // Basisklassen-Zeiger/Referenz hast..
  66.  
  67.   for (auto &p : vec)
  68.     bref.doIt(*p);
  69. }
Success #stdin #stdout 0s 3432KB
comments (?)
stdin
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Standard input is empty
stdout
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PBase: 0
P1: 1
P2: 2
https://ideone.com/b86vPv
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
secret

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