default_init_allocator.hpp

   1 #ifndef DEFAULT_INIT_ALLOCATOR_DOT_HPP
   2 #define DEFAULT_INIT_ALLOCATOR_DOT_HPP
   3
   4 // Allocator adaptor that interposes construct() calls to convert
   5 // value initialization into default initialization.
   6
   7 // <https://en.cppreference.com/w/cpp/container/vector/resize>
   8 // <https://stackoverflow.com/a/21028912/273767>
   9
  10 #include <memory>
  11
  12 template <typename T, typename A = std::allocator<T>>
  13 class default_init_allocator : public A {
  14   typedef std::allocator_traits<A> a_t;
  15
  16 public:
  17   template <typename U>
  18   struct rebind {
  19     using other
  20         = default_init_allocator<U, typename a_t::template rebind_alloc<U>>;
  21   };
  22
  23   using A::A;
  24
  25   template <typename U>
  26   void
  27   construct(U* ptr) noexcept(std::is_nothrow_default_constructible<U>::value)
  28   {
  29     ::new (static_cast<void*>(ptr)) U;
  30   }
  31   template <typename U, typename... Args>
  32   void construct(U* ptr, Args&&... args)
  33   {
  34     a_t::construct(static_cast<A&>(*this), ptr, std::forward<Args>(args)...);
  35   }
  36 };
  37
  38 #endif // DEFAULT_INIT_ALLOCATOR_DOT_HPP