optional.h

Go to the documentation of this file.

 
#ifndef DMLC_OPTIONAL_H_
#define DMLC_OPTIONAL_H_
 
#include <iostream>
#include <string>
#include <utility>
#include <algorithm>
 
#include "./base.h"
#include "./common.h"
#include "./logging.h"
#include "./type_traits.h"
 
namespace dmlc {
 
struct nullopt_t {
#if defined(_MSC_VER) && _MSC_VER < 1900
  explicit nullopt_t(int a) {}
#else
  constexpr explicit nullopt_t(int) {}
#endif
};
 
constexpr const nullopt_t nullopt = nullopt_t(0);
template <typename T> using decay_t = typename std::decay<T>::type;
template <bool B, typename T = void>
using enable_if_t = typename std::enable_if<B, T>::type;
 
struct in_place_t {
  explicit in_place_t() = default;  // NOLINT(*)
};
static constexpr in_place_t in_place{};
 
template <typename T> class optional;
template <typename T, typename U, typename Other>
using enable_constructor_from_other =
    enable_if_t<std::is_constructible<T, Other>::value &&
                !std::is_constructible<T, optional<U> &>::value &&
                !std::is_constructible<T, optional<U> &&>::value &&
                !std::is_convertible<optional<U> &, T>::value &&
                !std::is_convertible<optional<U> &&, T>::value &&
                !std::is_constructible<T, const optional<U> &>::value &&
                !std::is_constructible<T, const optional<U> &&>::value &&
                !std::is_convertible<const optional<U> &, T>::value &&
                !std::is_convertible<const optional<U> &&, T>::value>;
template <typename T, typename U>
using enable_constructor_from_value =
    enable_if_t<std::is_constructible<T, U &&>::value &&
                !std::is_same<decay_t<U>, in_place_t>::value &&
                !std::is_same<optional<T>, decay_t<U>>::value>;
template <typename T>
class optional {
 public:
  using value_type = T;
  optional() : is_none(true) {}
  optional(dmlc::nullopt_t) noexcept : is_none(true) {} // NOLINT(*)
  optional(const optional<T>& other) {
#pragma GCC diagnostic push
#if __GNUC__ >= 6
#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
#endif
    is_none = other.is_none;
    if (!is_none) {
      new (&val) T(other.value());
    }
#pragma GCC diagnostic pop
  }
  optional(optional &&other) noexcept(
      std::is_nothrow_move_constructible<T>::value
          &&std::is_nothrow_move_assignable<T>::value) {
    if (!other.has_value()) {
      reset();
    } else if (has_value()) {
      **this = std::move(*other);
    } else {
      new (&val) T(std::move(*other));
      is_none = false;
    }
  }
  template <typename... Args>
  explicit optional(
      enable_if_t<std::is_constructible<T, Args...>::value, in_place_t>,
      Args &&...args) {
    new (&val) T(std::forward<Args>(args)...);
    is_none = false;
  }
  template <typename U, typename... Args>
  explicit optional(
      enable_if_t<std::is_constructible<T, std::initializer_list<U> &,
                                        Args &&...>::value,
                  in_place_t>,
      std::initializer_list<U> ilist, Args &&...args) {
    construct(ilist, std::forward<Args>(args)...);
  }
  template <typename U = value_type,
            enable_if_t<std::is_convertible<U &&, T>::value> * = nullptr,
            enable_constructor_from_value<T, U> * = nullptr>
  optional(U &&other) noexcept {  // NOLINT(*)
    new (&val) T(std::forward<U>(other));
    is_none = false;
  }
  template <typename U = value_type,
            enable_if_t<!std::is_convertible<U &&, T>::value> * = nullptr,
            enable_constructor_from_value<T, U> * = nullptr>
  explicit optional(U &&other) noexcept {
    new (&val) T(std::forward<U>(other));
    is_none = false;
  }
  template <typename U,
            enable_constructor_from_other<T, U, const U &> * = nullptr,
            enable_if_t<std::is_convertible<const U &, T>::value> * = nullptr>
  optional(const optional<U> &other) {
    if (other.has_value()) {
      construct(*other);
    }
  }
  template <typename U,
            enable_constructor_from_other<T, U, const U &> * = nullptr,
            enable_if_t<!std::is_convertible<const U &, T>::value> * = nullptr>
  explicit optional(const optional<U> &other) {
    if (other.has_value()) {
      construct(*other);
    }
  }
  template <typename U, enable_constructor_from_other<T, U, U &&> * = nullptr,
            enable_if_t<std::is_convertible<U &&, T>::value> * = nullptr>
  optional(optional<U> &&other) {
    if (other.has_value()) {
      construct(std::move(*other));
    }
  }
  template <typename U, enable_constructor_from_other<T, U, U &&> * = nullptr,
            enable_if_t<!std::is_convertible<U &&, T>::value> * = nullptr>
  explicit optional(optional<U> &&other) {
    if (other.has_value()) {
      construct(std::move(*other));
    }
  }
  void reset() noexcept {
    if (!has_value())
      return;
    (**this).T::~T();
    is_none = true;
  }
  ~optional() {
    if (!is_none) {
      reinterpret_cast<T*>(&val)->~T();
    }
  }
  void swap(optional<T>& other) {
    std::swap(val, other.val);
    std::swap(is_none, other.is_none);
  }
  optional<T>& operator=(const T& value) {
    (optional<T>(value)).swap(*this);
    return *this;
  }
  optional<T>& operator=(const optional<T> &other) {
#pragma GCC diagnostic push
#if __GNUC__ >= 6
#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
#endif
    (optional<T>(other)).swap(*this);
    return *this;
#pragma GCC diagnostic pop
  }
  optional<T>& operator=(nullopt_t) {
    (optional<T>()).swap(*this);
    return *this;
  }
  T& operator*() {  // NOLINT(*)
    return *reinterpret_cast<T*>(&val);
  }
  const T& operator*() const {
    return *reinterpret_cast<const T*>(&val);
  }
  bool operator==(const optional<T>& other) const {
    return this->is_none == other.is_none &&
           (this->is_none == true || this->value() == other.value());
  }
  T &value() & {
    if (is_none) {
      throw std::logic_error("bad optional access");
    }
    return *reinterpret_cast<T *>(&val);
  }
  const T &value() const & {
    if (is_none) {
      throw std::logic_error("bad optional access");
    }
    return *reinterpret_cast<const T *>(&val);
  }
  T &&value() && {
    if (is_none) {
      throw std::logic_error("bad optional access");
    }
    return std::move(value());
  }
  const T &&value() const && {
    if (is_none) {
      throw std::logic_error("bad optional access");
    }
    return std::move(value());
  }
  explicit operator bool() const { return !is_none; }
  bool has_value() const { return operator bool(); }
 
 private:
  // whether this is none
  bool is_none = true;
  // on stack storage of value
  typename std::aligned_storage<sizeof(T), alignof(T)>::type val;
 
  template <typename... Args> void construct(Args &&...args) noexcept {
    new (std::addressof(val)) T(std::forward<Args>(args)...);
    is_none = false;
  }
};
 
template<typename T>
std::ostream &operator<<(std::ostream &os, const optional<T> &t) {
  if (t) {
    os << *t;
  } else {
    os << "None";
  }
  return os;
}
 
template<typename T>
std::istream &operator>>(std::istream &is, optional<T> &t) {
  char buf[4];
  std::streampos origin = is.tellg();
  is.read(buf, 4);
  if (is.fail() || buf[0] != 'N' || buf[1] != 'o' ||
      buf[2] != 'n' || buf[3] != 'e') {
    is.clear();
    is.seekg(origin);
    T x;
    is >> x;
    t = x;
    if (std::is_integral<T>::value && !is.eof() && is.peek() == 'L') is.get();
  } else {
    t = nullopt;
  }
  return is;
}
inline std::istream &operator>>(std::istream &is, optional<bool> &t) {
  // Discard initial whitespace
  while (isspace(is.peek()))
    is.get();
  // Extract chars that might be valid into a separate string, stopping
  // on whitespace or other non-alphanumerics such as ",)]".
  std::string s;
  while (isalnum(is.peek()))
    s.push_back(is.get());
 
  if (!is.fail()) {
    std::transform(s.begin(), s.end(), s.begin(), ::tolower);
    if (s == "1" || s == "true")
      t = true;
    else if (s == "0" || s == "false")
      t = false;
    else if (s == "none")
      t = nullopt;
    else
      is.setstate(std::ios::failbit);
  }
 
  return is;
}
 
DMLC_DECLARE_TYPE_NAME(optional<int>, "int or None");
DMLC_DECLARE_TYPE_NAME(optional<bool>, "boolean or None");
DMLC_DECLARE_TYPE_NAME(optional<float>, "float or None");
DMLC_DECLARE_TYPE_NAME(optional<double>, "double or None");
 
}  // namespace dmlc
 
namespace std {
template<typename T>
struct hash<dmlc::optional<T> > {
  size_t operator()(const dmlc::optional<T>& val) const {
    std::hash<bool> hash_bool;
    size_t res = hash_bool(val.has_value());
    if (val.has_value()) {
      res = dmlc::HashCombine(res, val.value());
    }
    return res;
  }
};
}  // namespace std
 
#endif  // DMLC_OPTIONAL_H_