flow_polymorphic_allocator.h

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#pragma once
#include "flow_default_memory_resource.h"
#include <cstddef>
 
namespace flow {

  template <typename T = std::byte>
  class PolymorphicAllocator {
  public:
    using value_type = T;

    PolymorphicAllocator() noexcept
      : resource_(&DefaultMemoryResource::getResource()) {
    }

    explicit PolymorphicAllocator(MemoryResource& resource) noexcept
      : resource_(&resource) {
    }

    template <typename U>
    PolymorphicAllocator(const PolymorphicAllocator<U>& allocator) noexcept
      : resource_(allocator.resource_) {
    }

    T* allocate(std::size_t count) {
      return static_cast<T*>(resource_->allocate(sizeof(T) * count, alignof(T)));
    }

    void deallocate(T* address, std::size_t count) noexcept {
      resource_->deallocate(address, sizeof(T) * count, alignof(T));
    }

    template <typename U, typename... Args>
    void construct(U* address, Args&&... args) {
      ::new (address) U(std::forward<Args>(args)...);
    }

    template <typename U>
    void destroy(U* address) noexcept {
      address->~U();
    }
 
  private:
    MemoryResource* resource_; 
 
    template <typename U>
    friend class PolymorphicAllocator;
 
    template <typename U>
    friend bool operator==(const PolymorphicAllocator<T>& lhs, const PolymorphicAllocator<U>& rhs) noexcept {
      return lhs.resource_ == rhs.resource_;
    }
 
    template <typename U>
    friend bool operator!=(const PolymorphicAllocator<T>& lhs, const PolymorphicAllocator<U>& rhs) noexcept {
      return !(lhs == rhs);
    }
  };
 
}