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  1. #include <utility>
  2.  
  3. template <typename ValueT>
  4. class default_accessor {
  5. public:
  6.     // Types.
  7.     typedef ValueT value_type;
  8.     typedef value_type& reference;
  9.     typedef const value_type& const_reference;
  10.  
  11.     // Constructors.
  12.     default_accessor(const_reference value_ref) : m_value_ref(value_ref)
  13.     {
  14.         // Do nothing.
  15.     }
  16.  
  17.     // Accessors.
  18.     const_reference operator()() const noexcept
  19.     {
  20.         return m_value_ref;
  21.     }
  22. private:
  23.     // Data.
  24.     const_reference m_value_ref;
  25. };
  26.  
  27. template <typename ValueT>
  28. class default_mutator {
  29. public:
  30.     // Types.
  31.     typedef ValueT value_type;
  32.     typedef value_type& reference;
  33.     typedef const value_type& const_reference;
  34.  
  35.     // Constructors.
  36.     default_mutator(reference value_ref) : m_value_ref(value_ref)
  37.     {
  38.         // Do nothing.
  39.     }
  40.  
  41.     // Mutators.
  42.     void operator()(const_reference value) noexcept
  43.     {
  44.         m_value_ref = value;
  45.     }
  46.  
  47.     void operator()(value_type&& value) noexcept
  48.     {
  49.         m_value_ref = std::move(value);
  50.     }
  51. private:
  52.     // Data.
  53.     reference m_value_ref;
  54. };
  55.  
  56. template <typename ValueT, class Accessor = default_accessor<ValueT>>
  57. class property_ro {
  58. public:
  59.     // Types.
  60.     typedef ValueT value_type;
  61.     typedef value_type& reference;
  62.     typedef const value_type& const_reference;
  63.     typedef Accessor accessor_type;
  64.  
  65.     // Constructors.
  66.     property_ro() : m_accessor(m_value)
  67.     {
  68.         // Do nothing.
  69.     }
  70.  
  71.     property_ro(accessor_type accessor) : m_accessor(accessor)
  72.     {
  73.         // Do nothing.
  74.     }
  75.  
  76.     property_ro(const reference value_ref) : m_accessor(value_ref)
  77.     {
  78.         // Do nothing.
  79.     }
  80.  
  81.     // Accessors.
  82.     const_reference get() noexcept
  83.     {
  84.         return m_accessor();
  85.     }
  86. private:
  87.     // Data.
  88.     ValueT m_value;
  89.     accessor_type m_accessor;
  90. };
  91.  
  92. template <typename ValueT, class Accessor = default_accessor<ValueT>, class Mutator = default_mutator<ValueT>>
  93. class property {
  94. public:
  95.     // Types.
  96.     typedef ValueT value_type;
  97.     typedef value_type& reference;
  98.     typedef const value_type& const_reference;
  99.     typedef Accessor accessor_type;
  100.     typedef Mutator mutator_type;
  101.  
  102.     // Constructors.
  103.     property() : m_accessor(m_value), m_mutator(m_value)
  104.     {
  105.         // Do nothing.
  106.     }
  107.  
  108.     property(accessor_type accessor, mutator_type mutator) : m_accessor(accessor), m_mutator(mutator)
  109.     {
  110.         // Do nothing.
  111.     }
  112.  
  113.     property(reference value_ref) : m_accessor(value_ref), m_mutator(value_ref)
  114.     {
  115.         // Do nothing.
  116.     }
  117.  
  118.     // Accessors.
  119.     const_reference get() const noexcept
  120.     {
  121.         return m_accessor();
  122.     }
  123.  
  124.     reference get() noexcept
  125.     {
  126.         return m_accessor();
  127.     }
  128.  
  129.     // Mutators.
  130.     void set(const_reference value)
  131.     {
  132.         m_mutator(value);
  133.     }
  134.  
  135.     void set(value_type&& value)
  136.     {
  137.         m_mutator(value);
  138.     }
  139.  
  140.     property& operator=(const_reference rhs)
  141.     {
  142.         const property& lhs(*this);
  143.         lhs.set(rhs);
  144.         return lhs;
  145.     }
  146.  
  147.     property& operator=(const property& rhs)
  148.     {
  149.         const property& lhs(*this);
  150.         lhs.set(rhs.get());
  151.         return lhs;
  152.     }
  153.  
  154.     property& operator=(const property_ro<value_type, accessor_type>& rhs)
  155.     {
  156.         const property& lhs(*this);
  157.         lhs.set(rhs.get());
  158.         return lhs;
  159.     }
  160. private:
  161.     // Data.
  162.     ValueT m_value;
  163.     accessor_type m_accessor;
  164.     mutator_type m_mutator;
  165. };
  166.  
  167. #include <iostream>
  168.  
  169. /// Custom accessor.
  170. class my_accessor {
  171. public:
  172.     my_accessor(const int& value_ref, int& counter_ref) : m_value_ref(value_ref), m_counter_ref(counter_ref)
  173.     {
  174.         // Do nothing.
  175.     }
  176.  
  177.     const int& operator()() noexcept
  178.     {
  179.         ++m_counter_ref;
  180.         return m_value_ref;
  181.     }
  182. private:
  183.     const int& m_value_ref;
  184.     int& m_counter_ref;
  185. };
  186.  
  187. /// Example showing a read-only property with a custom accessor which increments a counter whenever the property is
  188. /// accessed.
  189. class foo {
  190. public:
  191.     property_ro<int, my_accessor> readonly;
  192.     property_ro<int> times_accessed;
  193.  
  194.     foo(int value) : m_readonly(value), m_times_accessed(0), readonly(my_accessor(m_readonly, m_times_accessed)),
  195.                      times_accessed(m_times_accessed)
  196.     {
  197.         // Do nothing.
  198.     }
  199. private:
  200.     int m_readonly;
  201.     int m_times_accessed;
  202. };
  203.  
  204. int main()
  205. {
  206.     foo object(5);
  207.     for (int i = 0; i < 5; ++i) {
  208.         std::cout << "Times accessed: " << object.times_accessed.get() << '\n';
  209.         int tmp = object.readonly.get();
  210.     }
  211.     std::cout << "Times accessed: " << object.times_accessed.get() << std::endl;
  212.     return 0;
  213. }
Success #stdin #stdout 0s 3296KB
comments (?)
stdin 
Standard input is empty
stdout 
Times accessed: 0
Times accessed: 1
Times accessed: 2
Times accessed: 3
Times accessed: 4
Times accessed: 5
https://ideone.com/cRYmS0
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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