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  1. #include <iostream>
  2. #include <vector>
  3. #include <functional>
  4. #include <algorithm>
  5.  
  6. using namespace std;
  7.  
  8. //folgendes wäre Teil der Standardlibrary
  9. //nur minimale features implementiert (zeitgründe)
  10. class Integer {
  11. public:
  12.     typedef int BaseType;
  13.     int value;
  14.  
  15.     Integer(int value=0) : value(value) {}
  16.     Integer(Integer const& other) : value(other.value) {}
  17.  
  18.     Integer& operator=(Integer const& other) {
  19.         value=other.value;
  20.         return *this;
  21.     }
  22. };
  23.  
  24. Integer operator+(Integer const& lhs, Integer const& rhs) {
  25.     return Integer(lhs.value+rhs.value);
  26. }
  27.  
  28. class PositiveInteger : protected Integer {
  29. public:
  30.     typedef int BaseType;
  31.  
  32.     PositiveInteger(int value=0) : Integer(value) { if(value<0) throw "Negative Value"; }
  33.     PositiveInteger(Integer const& other) : Integer(other) { if(value<0) throw "Negative Value"; }
  34.  
  35.     PositiveInteger& operator=(Integer const& other) {
  36.         if(other.value < 0) throw "Negative Value";
  37.         value=other.value;
  38.         return *this;
  39.     }
  40.  
  41.     operator Integer() { return *this; }
  42. };
  43.  
  44.  
  45.  
  46. template<typename T>
  47. class Vector {
  48. private:
  49.     vector<T> impl;
  50.  
  51. public:
  52.     void add(T const& val) {
  53.         impl.push_back(val);
  54.     }
  55.  
  56.     template<typename F>
  57.     void for_each(F f) {
  58.         for(auto& obj : impl) {
  59.             f(obj);
  60.         }
  61.     }
  62. };
  63.  
  64. template<typename T>
  65. class ChangeObserver : public Vector<function<void(T const&, T const&)> > {
  66. public:
  67.     void change(T const& oldVal, T const& newVal) {
  68.         this->for_each([&](function<void(T const&, T const&)> f) { f(oldVal, newVal); });
  69.     }
  70. };
  71.  
  72. template<typename ValueType>
  73. class ChangeObservableArithmeticType : private ValueType, public ChangeObserver<ValueType> {
  74. public:
  75.     typedef typename ValueType::BaseType BaseType;
  76.     ChangeObservableArithmeticType(typename ValueType::BaseType value=0) : ValueType(value) {}
  77.     ChangeObservableArithmeticType(ChangeObservableArithmeticType const& other) : ValueType(other) {}
  78.     ChangeObservableArithmeticType(ValueType const& other) : ValueType(other) {}
  79.  
  80.     ChangeObservableArithmeticType& operator=(ChangeObservableArithmeticType const& other) {
  81.         this->change(*this, other);
  82.         this->value=other.value;
  83.         return *this;
  84.     }
  85.  
  86.     operator ValueType() {
  87.         return *this;
  88.     }
  89. };
  90.  
  91. class Radius : public ChangeObservableArithmeticType<PositiveInteger> {
  92. };
  93.  
  94. class Kreis : public Radius {
  95. public:
  96.     Kreis() {
  97.         add([&](::PositiveInteger const&, ::PositiveInteger const&) {
  98.             redraw();
  99.         });
  100.  
  101.         redraw();
  102.     }
  103.  
  104.     void redraw() {
  105.         cout<<"Radius changed, Kreis redrawn\n";
  106.     }
  107. };
  108.  
  109. int main() {
  110.     //2x redraw ausführen:
  111.     Kreis k;
  112.     k.ChangeObservableArithmeticType::operator=(7);
  113.  
  114.     try {
  115.         k.ChangeObservableArithmeticType::operator=(-7);
  116.     } catch(...) {
  117.         cout<<"Error\n";
  118.     }
  119.  
  120.     return 0;
  121. }
  122.  
  123.  
Success #stdin #stdout 0s 2988KB
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Radius changed, Kreis redrawn
Radius changed, Kreis redrawn
Error
https://ideone.com/hHs59f
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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