cpp-descriptive-pointers/include/pointers/const_ptr.hpp

//
//  const_ptr.hpp
//  pointers
//
//  Created by Sam Jaffe on 1/5/17.
//

#pragma once
#include <memory>

#include "detail/compare.hpp"
#include "detail/get_ptr.hpp"
#include "pointer_fwd.hpp"

namespace pointers {

  template <typename P>
  class const_ptr : private detail::get_ptr<P>,
                    public detail::pointer_compare<const_ptr<P>> {
  public:
    using element_type = typename std::pointer_traits<P>::element_type;
    using pointer = element_type const *;
    using reference = element_type const &;

    const_ptr() noexcept : _ptr(nullptr) {}
    const_ptr(P const & p) noexcept(
        std::is_nothrow_copy_constructible<P>::value)
        : _ptr(p) {}
    const_ptr(P && p) noexcept(std::is_nothrow_move_constructible<P>::value)
        : _ptr(std::move(p)) {}
    template <typename Y, typename = typename std::enable_if<
                              std::is_constructible<P, Y>::value>::type>
    const_ptr(Y const & p) : _ptr(p) {}
    template <typename Y, typename = typename std::enable_if<
                              std::is_constructible<P, Y>::value>::type>
    const_ptr(Y && p) : _ptr(std::forward<Y>(p)) {}

    template <typename Y>
    explicit operator const_ptr<Y>() const
        noexcept(std::is_nothrow_constructible<P, Y>::value) {
      return _ptr;
    }

    operator bool() const noexcept { return static_cast<bool>(_ptr); }

    reference operator*() const noexcept(noexcept(*_ptr)) { return *_ptr; }
    pointer get() const noexcept(noexcept(detail::get_ptr<P>::get(_ptr))) {
      return detail::get_ptr<P>::get(_ptr);
    }
    pointer operator->() const noexcept(noexcept(get())) { return get(); }

  private:
    P _ptr;
  };

}