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  1. #include <unordered_map>
  2. #include <memory>
  3.  
  4. template<typename T>
  5. class TestAllocator;
  6.  
  7. template<>
  8. class TestAllocator<void>
  9. {
  10. public:
  11.   typedef void * pointer;
  12.   typedef const void * const_pointer;
  13.   typedef void value_type;
  14.   typedef size_t size_type;
  15.   typedef ptrdiff_t difference_type;
  16.   //typedef T & reference; not possible for void
  17.   //typedef const T & const_reference; not possible for void
  18.  
  19.   template<typename U>
  20.   struct rebind
  21.   {
  22.     typedef TestAllocator<U> other;  
  23.   };
  24. };
  25.  
  26. template<typename T>
  27. class TestAllocator
  28. {
  29. public:
  30.   typedef T * pointer;
  31.   typedef const T * const_pointer;
  32.   typedef T & reference;
  33.   typedef const T & const_reference;
  34.   typedef T value_type;
  35.   typedef size_t size_type;
  36.   typedef ptrdiff_t difference_type;
  37.  
  38.   template<typename U>
  39.   struct rebind
  40.   {
  41.     typedef TestAllocator<U> other;  
  42.   };
  43.  
  44.   TestAllocator() { }
  45.   template<typename U>
  46.   TestAllocator(const TestAllocator<U> &other) { }
  47.  
  48.   pointer allocate(int n, pointer hint=0) { return new T[n]; }
  49.   pointer deallocate(pointer p, size_t n) { delete[] p; }
  50.   pointer address(reference x) { return &x; } // hack! should be std::addressof(x);
  51.   void construct(pointer p, const_reference val) { new (p) value_type(val); }
  52.   void destroy(pointer p) { p->~value_type(); }
  53. };
  54.  
  55. struct Foo
  56. {
  57.     int a, b;
  58.     bool operator <(const Foo &r) const
  59.     {
  60.         return a < r.a;
  61.     }
  62. };
  63.  
  64. struct Bar { float a, b; };
  65.  
  66. struct TrivialHash
  67. {
  68.     size_t operator()(const Foo &a) const
  69.     {
  70.         return a.a;
  71.     }
  72. };
  73.  
  74. struct TrivialEqual
  75. {
  76.     bool operator()(const Foo &a, const Foo &b) const
  77.     {
  78.         return a.a == b.a;
  79.     }
  80. };
  81.  
  82. typedef std::unordered_map<
  83.   Foo, Bar,
  84.   TrivialHash,
  85.   TrivialEqual,
  86.   TestAllocator<int>
  87. > TestContainer;
  88.  
  89. int main()
  90. {
  91.     TestContainer x;
  92.     x.insert(TestContainer::value_type(Foo(), Bar()));
  93.     return 0;
  94. }
  95.  
Success #stdin #stdout 0s 3056KB
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https://ideone.com/vsqJRG
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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