dllink.hpp

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#pragma once
 
#include <cassert>
#include <utility>  // for std::move()
 
// Forward declaration for begin() end()
class RDllist;
class RDllIterator;
 
#pragma pack(push, 1)
template <typename T> class Dllink {
  public:
    Dllink* next{this}; 
    Dllink* prev{this}; 
    T data{};           
    constexpr explicit Dllink(T dat) noexcept : data{std::move(dat)} {
        static_assert(sizeof(Dllink) <= 24, "keep this class small");
    }
 
    constexpr Dllink() = default;
    ~Dllink() = default;
    Dllink(const Dllink&) = delete;                     // don't copy
    auto operator=(const Dllink&) -> Dllink& = delete;  // don't assign
    constexpr Dllink(Dllink&&) noexcept = default;
    constexpr auto operator=(Dllink&&) noexcept -> Dllink& = delete;  // don't assign
 
    constexpr auto lock() noexcept -> void { this->next = this; }
 
    constexpr auto is_locked() const noexcept -> bool { return this->next == this; }
 
    constexpr auto detach() noexcept -> void {
        assert(!this->is_locked());
        const auto n = this->next;
        const auto p = this->prev;
        p->next = n;
        n->prev = p;
    }
 
  private:
    constexpr auto attach(Dllink& node) noexcept -> void {
        node.next = this->next;
        this->next->prev = &node;
        this->next = &node;
        node.prev = this;
    }
};
#pragma pack(pop)