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  1. #include <iostream>
  2. #include <utility>
  3. #include <string>
  4.  
  5. class Var
  6. {
  7. private:
  8.     struct controlBlockBase
  9.     {
  10.         unsigned short uses;
  11.  
  12.         controlBlockBase() : uses(1) { }
  13.         virtual ~controlBlockBase() { }
  14.     };
  15.  
  16.     template <class K>
  17.     struct controlBlockImpl : controlBlockBase
  18.     {
  19.         K value;
  20.         controlBlockImpl(const K &val) : controlBlockBase(), value(val) {}
  21.     };
  22.  
  23.     controlBlockBase *cb;
  24.  
  25. public:
  26.     Var() : cb(nullptr) {
  27.     	std::cout << "Var default constructed" << std::endl;
  28.     }
  29.  
  30.     template<typename K>
  31.     Var(const K &value) : cb(new controlBlockImpl<K>(value)) { 
  32.     	std::cout << "Var value constructed" << std::endl;
  33.     }
  34.  
  35.     Var(const Var &obj) : cb(obj.cb) {
  36.         if (cb) {
  37.             ++(cb->uses);
  38.         }
  39.         std::cout << "Var copy constructed" << std::endl;
  40.     }
  41.  
  42.     Var(Var &&obj) : cb(nullptr) {
  43.         obj.swap(*this);
  44.         std::cout << "Var move constructed" << std::endl;
  45.     }
  46.  
  47.     ~Var() {
  48.         if ((cb) && ((cb->uses -= 1) <= 0)) {
  49.             delete cb;
  50.             cb = nullptr;
  51.         }
  52.         std::cout << "Var destructed" << std::endl;
  53.     }
  54.  
  55.     Var& operator=(const Var& obj) {
  56.         if (this != &obj) {
  57.             Var(obj).swap(*this);
  58.         }
  59.         std::cout << "Var copy assigned" << std::endl;
  60.         return *this;
  61.     }
  62.  
  63.     Var& operator=(Var &&obj) {
  64.         obj.swap(*this);
  65.         std::cout << "Var move assigned" << std::endl;
  66.         return *this;
  67.     }
  68.  
  69.     void swap(Var &other) {
  70.     	std::swap(cb, other.cb);
  71.     }
  72.  
  73.     unsigned short getUses() const {
  74.     	return (cb) ? cb->uses : 0;
  75.     }
  76. };
  77.  
  78. namespace std {
  79. 	void swap(Var &v1, Var &v2) {
  80. 		v1.swap(v2);
  81. 	}
  82. }
  83.  
  84. class C
  85. {
  86. public:
  87.     Var var;
  88.  
  89.     C() {
  90.     	std::cout << "C default constructed" << std::endl;
  91.     }
  92.  
  93.     C(const C &c) : var(c.var) {
  94.     	std::cout << "C copy constructed" << std::endl;
  95.     }
  96.  
  97.     C(C &&c) : var(std::move(c.var)) {
  98.     	std::cout << "C move constructed" << std::endl;
  99.     }
  100.  
  101.     C(Var var) : var(var) {
  102.     	std::cout << "C value constructed" << std::endl;
  103.     }
  104.  
  105.     ~C() {
  106.     	std::cout << "C destructed" << std::endl;
  107.     }
  108.  
  109.     C& operator=(const C &c) {
  110.     	if (this != &c) {
  111.     		 C tmp(c);
  112.     		 std::swap(var, tmp.var);
  113.     	}
  114.     	std::cout << "C copy assigned" << std::endl;
  115.     	return *this;
  116.     }
  117.  
  118.     C& operator=(C &&c) {
  119.         std::swap(var, c.var);
  120.     	std::cout << "C move assigned" << std::endl;
  121.     	return *this;
  122.     }
  123. };
  124.  
  125. class MyString
  126. {
  127. public:
  128.     std::string str;
  129.  
  130.     MyString() {
  131.     	std::cout << "MyString default constructed" << std::endl;
  132.     }
  133.  
  134.     MyString(const char *s) : str(s) {
  135.     	std::cout << "MyString value constructed" << std::endl;
  136.     }
  137.  
  138.     MyString(const std::string &s) : str(s) {
  139.     	std::cout << "MyString value constructed" << std::endl;
  140.     }
  141.  
  142.     MyString(const MyString &s) : str(s.str) {
  143.     	std::cout << "MyString copy constructed" << std::endl;
  144.     }
  145.  
  146.     MyString(MyString &&s) : str(std::move(s.str)) {
  147.     	std::cout << "MyString move constructed" << std::endl;
  148.     }
  149.  
  150.     ~MyString() {
  151.     	std::cout << "MyString destructed" << std::endl;
  152.     }
  153.  
  154.     MyString& operator=(const MyString &s) {
  155.     	if (this != &s) {
  156.     		 str = s.str;
  157.     	}
  158.     	std::cout << "MyString copy assigned" << std::endl;
  159.     	return *this;
  160.     }
  161.  
  162.     MyString& operator=(MyString &&s) {
  163.         str = std::move(s.str);
  164.     	std::cout << "MyString move assigned" << std::endl;
  165.     	return *this;
  166.     }
  167. };
  168.  
  169. void test()
  170. {
  171.     MyString string = "Hello";
  172.     Var var1 = Var(string);
  173.     std::cout << "var1 uses=" << var1.getUses() << std::endl;
  174.     C c = C(var1);
  175.     std::cout << "var1 uses=" << var1.getUses() << std::endl;
  176.     Var var2 = Var(c);
  177.     std::cout << "var1 uses=" << var1.getUses() << std::endl;
  178.     std::cout << "var2 uses=" << var2.getUses() << std::endl;
  179. }
  180.  
  181. int main() {
  182.     test();
  183.     return 0;
  184. }
Success #stdin #stdout 0s 15248KB
comments (?)
stdin
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Standard input is empty
stdout
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MyString value constructed
MyString copy constructed
Var value constructed
var1 uses=1
Var copy constructed
Var copy constructed
C value constructed
Var destructed
var1 uses=2
Var copy constructed
C copy constructed
Var value constructed
var1 uses=3
var2 uses=1
C destructed
Var destructed
Var destructed
C destructed
Var destructed
MyString destructed
Var destructed
MyString destructed
https://ideone.com/5oFWS6
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
public

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