TVAlloc.h

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#ifndef TVAlloc_included
#define TVAlloc_included
 
/*! Allocator adaptor that intercepts the 'construct' calls to convert value initialization into default initialization
 * Written by Casey Carter (@codercasey)
 * Taken from https://hackingcpp.com/cpp/recipe/uninitialized_numeric_array.html
 *
 * This allows "std::vector<T>(30)" to only allocate, not initialize, the data.
 */
template< typename T, typename Alloc = std::allocator<T> >
class TVAlloc : public Alloc
{
  using a_t = std::allocator_traits<Alloc>;
public:
  // Obtain alloc<U> where U != T
  template<typename U>
  struct rebind
  {
    using other = TVAlloc<U, typename a_t::template rebind_alloc<U> >;
  };
 
  // Make inherited ctors visible
  using Alloc::Alloc;
 
  // Ddefault-construct objects - WITHOUT initialisation!
  template<typename U>
  void construct (U* ptr)     noexcept(    std::is_nothrow_default_constructible<      U>::value)
  {
    ::new(static_cast<void*>(ptr)) U; // 'placement new':
  }
 
  // Construct with ctor arguments
  template<typename U, typename... Args>
  void construct (U* ptr, Args&& ... args)
  {
    a_t::construct(
      static_cast<Alloc&>(*this),
      ptr, std::forward<Args>(args)...);
  }
 
};
 
#endif /* TVAlloc_included */