cpp-descriptive-pointers/not_null.hpp

//
//  not_null.hpp
//  pointer
//
//  Created by Sam Jaffe on 9/24/15.
//
//

#pragma once

#include <memory>

#include "pointer_fwd.hpp"
#include "ptr_compare.hpp"
#include "maybe_null.hpp"

template <typename P> class not_null<std::weak_ptr<P>>; // A weak_ptr cannot be a not_null

template <typename P>
class not_null {
public:
  using element_type = typename std::pointer_traits<P>::element_type;
  using pointer = element_type *;
  using reference = element_type &;
  
  explicit not_null(std::nullptr_t) = delete;
  explicit not_null(int) = delete;
  not_null(P const & p) : _ptr(p) { validate(); }
  not_null(P && p) : _ptr(std::move(p)) { validate(); }
  not_null(not_null const&) noexcept(detail::is_nt_cc<P>::value) = default;
  not_null(not_null &&) = delete;
  
  template <typename Y>
  explicit operator maybe_null<Y>() const noexcept(detail::is_nt_c<Y, P>::value) {
    return _ptr;
  }
  template <typename Y>
  explicit operator not_null<Y>() const noexcept(detail::is_nt_c<Y, P>::value) {
    return _ptr;
  }

  not_null& operator=(not_null const&) noexcept(detail::is_nt_ca<P>::value) = default;
  not_null& operator=(not_null &&) = delete;
  
  operator bool() const noexcept { return true; }
  
  pointer get() const noexcept { return detail::get_ptr<P>().get(_ptr); }
  reference operator*() const noexcept { return *_ptr; }
  pointer operator->() const noexcept { return get(); }
  
  void reset( P const & p ) { operator=(not_null(p)); }
  void reset( P && p ) { operator=(not_null(std::forward(p))); }
private:
  void validate() {
    if (get() == nullptr) {
      throw null_pointer_exception{"not_null<P> cannot be null"};
    }
  }
  P _ptr;
};

POINTER_TEMPLATE_COMPARE( not_null )