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  1. #include <iostream>
  2. #include <memory>
  3.  
  4. class Container {
  5.  
  6.     struct Var;
  7.     typedef std::ostream Out;
  8.     typedef std::shared_ptr<Var> VarPtr;
  9.     std::shared_ptr<VarPtr> varptr_;
  10.  
  11.     struct BadType {};
  12.  
  13.     struct Var {
  14.         virtual ~Var () = default;
  15.         virtual Out & print (Out &os) { return os << "(BadType)"; }
  16.         virtual void set (int) { throw BadType(); }
  17.         virtual void set (const std::string &) { throw BadType(); }
  18.     };
  19.  
  20.     struct VarInteger : Var {
  21.         int data;
  22.         VarInteger (int v) : data(v) {}
  23.         Out & print (Out &os) { return os << data; }
  24.         void set (int v) throw() { data = v; }
  25.     };
  26.  
  27.     struct VarString : Var {
  28.         std::string data;
  29.         VarString (const std::string &v) : data(v) {}
  30.         Out & print (Out &os) { return os << data; }
  31.         void set (const std::string &v) throw() { data = v; }
  32.     };
  33.  
  34.     static VarPtr make_var () { return std::make_shared<Var>(); }
  35.     static VarPtr make_var (int v) { return std::make_shared<VarInteger>(v); }
  36.     static VarPtr make_var (const std::string &v) {
  37.         return std::make_shared<VarString>(v);
  38.     }
  39.  
  40.     VarPtr & var () { return *varptr_; }
  41.     const VarPtr & var () const { return *varptr_; }
  42.  
  43. public:
  44.  
  45.     Container () : varptr_(std::make_shared<VarPtr>(make_var())) {}
  46.     Container (int v) : varptr_(std::make_shared<VarPtr>(make_var(v))) {}
  47.     Container (const std::string &v)
  48.         : varptr_(std::make_shared<VarPtr>(make_var(v))) {}
  49.  
  50.     void set (int v) {
  51.         try { var()->set(v); }
  52.         catch (BadType) { var() = make_var(v); }
  53.     }
  54.  
  55.     void set (const std::string &v) {
  56.         try { var()->set(v); }
  57.         catch (BadType) { var() = make_var(v); }
  58.     }
  59.  
  60.     void createLink (const Container &val) { varptr_ = val.varptr_; }
  61.  
  62.     friend Out & operator << (Out &os, const Container &val) {
  63.         return val.var()->print(os);
  64.     }
  65. };
  66.  
  67. int main () {
  68.     Container cont1("some value");
  69.     Container cont2;
  70.     cont2.createLink(cont1);
  71.     std::cout << cont1 << '\n';
  72.     cont2.set(20);
  73.     std::cout << cont1 << '\n';
  74. }
Success #stdin #stdout 0s 3236KB
comments (?)
stdin 
Standard input is empty
stdout 
some value
20
https://ideone.com/VYdubh
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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