v1.4.4

source/core/StarMaybe.hpp

@@ -0,0 +1,400 @@
+#ifndef STAR_MAYBE_HPP
+#define STAR_MAYBE_HPP
+
+#include "StarException.hpp"
+#include "StarHash.hpp"
+
+namespace Star {
+
+STAR_EXCEPTION(InvalidMaybeAccessException, StarException);
+
+template <typename T>
+class Maybe {
+public:
+  typedef T* PointerType;
+  typedef T const* PointerConstType;
+  typedef T& RefType;
+  typedef T const& RefConstType;
+
+  Maybe();
+
+  Maybe(T const& t);
+  Maybe(T&& t);
+
+  Maybe(Maybe const& rhs);
+  Maybe(Maybe&& rhs);
+  template <typename T2>
+  Maybe(Maybe<T2> const& rhs);
+
+  ~Maybe();
+
+  Maybe& operator=(Maybe const& rhs);
+  Maybe& operator=(Maybe&& rhs);
+  template <typename T2>
+  Maybe& operator=(Maybe<T2> const& rhs);
+
+  bool isValid() const;
+  bool isNothing() const;
+  explicit operator bool() const;
+
+  PointerConstType ptr() const;
+  PointerType ptr();
+
+  PointerConstType operator->() const;
+  PointerType operator->();
+
+  RefConstType operator*() const;
+  RefType operator*();
+
+  bool operator==(Maybe const& rhs) const;
+  bool operator!=(Maybe const& rhs) const;
+  bool operator<(Maybe const& rhs) const;
+
+  RefConstType get() const;
+  RefType get();
+
+  // Get either the contents of this Maybe or the given default.
+  T value(T def = T()) const;
+
+  // Get either this value, or if this value is none the given value.
+  Maybe orMaybe(Maybe const& other) const;
+
+  // Takes the value out of this Maybe, leaving it Nothing.
+  T take();
+
+  // If this Maybe is set, assigns it to t and leaves this Maybe as Nothing.
+  bool put(T& t);
+
+  void set(T const& t);
+  void set(T&& t);
+
+  template <typename... Args>
+  void emplace(Args&&... t);
+
+  void reset();
+
+  // Apply a function to the contained value if it is not Nothing.
+  template <typename Function>
+  void exec(Function&& function);
+
+  // Functor map operator.  If this maybe is not Nothing, then applies the
+  // given function to it and returns the result, otherwise returns Nothing (of
+  // the type the function would normally return).
+  template <typename Function>
+  auto apply(Function&& function) const -> Maybe<typename std::decay<decltype(function(std::declval<T>()))>::type>;
+
+  // Monadic bind operator.  Given function should return another Maybe.
+  template <typename Function>
+  auto sequence(Function function) const -> decltype(function(std::declval<T>()));
+
+private:
+  union {
+    T m_data;
+  };
+
+  bool m_initialized;
+};
+
+template <typename T>
+std::ostream& operator<<(std::ostream& os, Maybe<T> const& v);
+
+template <typename T>
+struct hash<Maybe<T>> {
+  size_t operator()(Maybe<T> const& m) const;
+  hash<T> hasher;
+};
+
+template <typename T>
+Maybe<T>::Maybe()
+  : m_initialized(false) {}
+
+template <typename T>
+Maybe<T>::Maybe(T const& t)
+  : Maybe() {
+  new (&m_data) T(t);
+  m_initialized = true;
+}
+
+template <typename T>
+Maybe<T>::Maybe(T&& t)
+  : Maybe() {
+  new (&m_data) T(forward<T>(t));
+  m_initialized = true;
+}
+
+template <typename T>
+Maybe<T>::Maybe(Maybe const& rhs)
+  : Maybe() {
+  if (rhs.m_initialized) {
+    new (&m_data) T(rhs.m_data);
+    m_initialized = true;
+  }
+}
+
+template <typename T>
+Maybe<T>::Maybe(Maybe&& rhs)
+  : Maybe() {
+  if (rhs.m_initialized) {
+    new (&m_data) T(move(rhs.m_data));
+    m_initialized = true;
+    rhs.reset();
+  }
+}
+
+template <typename T>
+template <typename T2>
+Maybe<T>::Maybe(Maybe<T2> const& rhs)
+  : Maybe() {
+  if (rhs) {
+    new (&m_data) T(*rhs);
+    m_initialized = true;
+  }
+}
+
+template <typename T>
+Maybe<T>::~Maybe() {
+  reset();
+}
+
+template <typename T>
+Maybe<T>& Maybe<T>::operator=(Maybe const& rhs) {
+  if (&rhs == this)
+    return *this;
+
+  if (rhs)
+    emplace(*rhs);
+  else
+    reset();
+
+  return *this;
+}
+
+template <typename T>
+template <typename T2>
+Maybe<T>& Maybe<T>::operator=(Maybe<T2> const& rhs) {
+  if (rhs)
+    emplace(*rhs);
+  else
+    reset();
+
+  return *this;
+}
+
+template <typename T>
+Maybe<T>& Maybe<T>::operator=(Maybe&& rhs) {
+  if (&rhs == this)
+    return *this;
+
+  if (rhs)
+    emplace(rhs.take());
+  else
+    reset();
+
+  return *this;
+}
+
+template <typename T>
+bool Maybe<T>::isValid() const {
+  return m_initialized;
+}
+
+template <typename T>
+bool Maybe<T>::isNothing() const {
+  return !m_initialized;
+}
+
+template <typename T>
+Maybe<T>::operator bool() const {
+  return m_initialized;
+}
+
+template <typename T>
+auto Maybe<T>::ptr() const -> PointerConstType {
+  if (m_initialized)
+    return &m_data;
+  return nullptr;
+}
+
+template <typename T>
+auto Maybe<T>::ptr() -> PointerType {
+  if (m_initialized)
+    return &m_data;
+  return nullptr;
+}
+
+template <typename T>
+auto Maybe<T>::operator-> () const -> PointerConstType {
+  if (!m_initialized)
+    throw InvalidMaybeAccessException();
+
+  return &m_data;
+}
+
+template <typename T>
+auto Maybe<T>::operator->() -> PointerType {
+  if (!m_initialized)
+    throw InvalidMaybeAccessException();
+
+  return &m_data;
+}
+
+template <typename T>
+auto Maybe<T>::operator*() const -> RefConstType {
+  return get();
+}
+
+template <typename T>
+auto Maybe<T>::operator*() -> RefType {
+  return get();
+}
+
+template <typename T>
+bool Maybe<T>::operator==(Maybe const& rhs) const {
+  if (!m_initialized && !rhs.m_initialized)
+    return true;
+  if (m_initialized && rhs.m_initialized)
+    return get() == rhs.get();
+  return false;
+}
+
+template <typename T>
+bool Maybe<T>::operator!=(Maybe const& rhs) const {
+  return !operator==(rhs);
+}
+
+template <typename T>
+bool Maybe<T>::operator<(Maybe const& rhs) const {
+  if (m_initialized && rhs.m_initialized)
+    return get() < rhs.get();
+  if (!m_initialized && rhs.m_initialized)
+    return true;
+  return false;
+}
+
+template <typename T>
+auto Maybe<T>::get() const -> RefConstType {
+  if (!m_initialized)
+    throw InvalidMaybeAccessException();
+
+  return m_data;
+}
+
+template <typename T>
+auto Maybe<T>::get() -> RefType {
+  if (!m_initialized)
+    throw InvalidMaybeAccessException();
+
+  return m_data;
+}
+
+template <typename T>
+T Maybe<T>::value(T def) const {
+  if (m_initialized)
+    return m_data;
+  else
+    return def;
+}
+
+template <typename T>
+Maybe<T> Maybe<T>::orMaybe(Maybe const& other) const {
+  if (m_initialized)
+    return *this;
+  else
+    return other;
+}
+
+template <typename T>
+T Maybe<T>::take() {
+  if (!m_initialized)
+    throw InvalidMaybeAccessException();
+
+  T val(move(m_data));
+
+  reset();
+
+  return val;
+}
+
+template <typename T>
+bool Maybe<T>::put(T& t) {
+  if (m_initialized) {
+    t = move(m_data);
+
+    reset();
+
+    return true;
+  } else {
+    return false;
+  }
+}
+
+template <typename T>
+void Maybe<T>::set(T const& t) {
+  emplace(t);
+}
+
+template <typename T>
+void Maybe<T>::set(T&& t) {
+  emplace(forward<T>(t));
+}
+
+template <typename T>
+template <typename... Args>
+void Maybe<T>::emplace(Args&&... t) {
+  reset();
+
+  new (&m_data) T(forward<Args>(t)...);
+  m_initialized = true;
+}
+
+template <typename T>
+void Maybe<T>::reset() {
+  if (m_initialized) {
+    m_initialized = false;
+    m_data.~T();
+  }
+}
+
+template <typename T>
+template <typename Function>
+auto Maybe<T>::apply(Function&& function) const
+    -> Maybe<typename std::decay<decltype(function(std::declval<T>()))>::type> {
+  if (!isValid())
+    return {};
+  return function(get());
+}
+
+template <typename T>
+template <typename Function>
+void Maybe<T>::exec(Function&& function) {
+  if (isValid())
+    function(get());
+}
+
+template <typename T>
+template <typename Function>
+auto Maybe<T>::sequence(Function function) const -> decltype(function(std::declval<T>())) {
+  if (!isValid())
+    return {};
+  return function(get());
+}
+
+template <typename T>
+std::ostream& operator<<(std::ostream& os, Maybe<T> const& v) {
+  if (v)
+    return os << "Just (" << *v << ")";
+  else
+    return os << "Nothing";
+}
+
+template <typename T>
+size_t hash<Maybe<T>>::operator()(Maybe<T> const& m) const {
+  if (!m)
+    return 0;
+  else
+    return hasher(*m);
+}
+
+}
+
+#endif