X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=folly%2FOptional.h;h=f8d39cb8cc39e0ce9b4407041e5a9d329be7e825;hb=ea815395588bf55ce57f505e05f5df469edf3436;hp=871357ceabb3168b29b3da49c13886482d1d11dd;hpb=fd20c97c69af72155fc5d611630b4799eeda6db8;p=folly.git

diff --git a/folly/Optional.h b/folly/Optional.h
index 871357ce..f8d39cb8 100644
--- a/folly/Optional.h
+++ b/folly/Optional.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 Facebook, Inc.
+ * Copyright 2017 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -14,8 +14,7 @@
  * limitations under the License.
  */
 
-#ifndef FOLLY_OPTIONAL_H_
-#define FOLLY_OPTIONAL_H_
+#pragma once
 
 /*
  * Optional - For conditional initialization of values, like boost::optional,
@@ -54,76 +53,84 @@
  *    cout << *v << endl;
  *  }
  */
-#include <utility>
-#include <cassert>
+
 #include <cstddef>
+#include <functional>
+#include <new>
+#include <stdexcept>
 #include <type_traits>
+#include <utility>
 
-#include <boost/operators.hpp>
+#include <folly/Launder.h>
+#include <folly/Portability.h>
+#include <folly/Utility.h>
 
 namespace folly {
 
-namespace detail { struct NoneHelper {}; }
+namespace detail {
+struct NoneHelper {};
+
+// Allow each translation unit to control its own -fexceptions setting.
+// If exceptions are disabled, std::terminate() will be called instead of
+// throwing OptionalEmptyException when the condition fails.
+[[noreturn]] void throw_optional_empty_exception();
+}
 
 typedef int detail::NoneHelper::*None;
 
 const None none = nullptr;
 
-/**
- * gcc-4.7 warns about use of uninitialized memory around the use of storage_
- * even though this is explicitly initialized at each point.
- */
-#if defined(__GNUC__) && !defined(__clang__)
-# pragma GCC diagnostic push
-# pragma GCC diagnostic ignored "-Wuninitialized"
-# pragma GCC diagnostic ignored "-Wpragmas"
-# pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
-#endif // __GNUC__
-
-template<class Value>
-class Optional : boost::totally_ordered<Optional<Value>,
-                 boost::totally_ordered<Optional<Value>, Value>> {
-  typedef void (Optional::*bool_type)() const;
-  void truthy() const {};
+class OptionalEmptyException : public std::runtime_error {
  public:
-  static_assert(!std::is_reference<Value>::value,
-                "Optional may not be used with reference types");
+  OptionalEmptyException()
+      : std::runtime_error("Empty Optional cannot be unwrapped") {}
+};
 
-  Optional()
-    : hasValue_(false) {
-  }
+template <class Value>
+class Optional {
+ public:
+  typedef Value value_type;
+
+  static_assert(
+      !std::is_reference<Value>::value,
+      "Optional may not be used with reference types");
+  static_assert(
+      !std::is_abstract<Value>::value,
+      "Optional may not be used with abstract types");
 
-  Optional(const Optional& src) {
+  Optional() noexcept {}
+
+  Optional(const Optional& src) noexcept(
+      std::is_nothrow_copy_constructible<Value>::value) {
     if (src.hasValue()) {
-      construct(src.value());
-    } else {
-      hasValue_ = false;
+      storage_.construct(src.value());
     }
   }
 
-  Optional(Optional&& src) {
+  Optional(Optional&& src) noexcept(
+      std::is_nothrow_move_constructible<Value>::value) {
     if (src.hasValue()) {
-      construct(std::move(src.value()));
+      storage_.construct(std::move(src.value()));
       src.clear();
-    } else {
-      hasValue_ = false;
     }
   }
 
-  /* implicit */ Optional(const None& empty)
-    : hasValue_(false) {
-  }
+  /* implicit */ Optional(const None&) noexcept {}
 
-  /* implicit */ Optional(Value&& newValue) {
-    construct(std::move(newValue));
+  /* implicit */ Optional(Value&& newValue) noexcept(
+      std::is_nothrow_move_constructible<Value>::value) {
+    storage_.construct(std::move(newValue));
   }
 
-  /* implicit */ Optional(const Value& newValue) {
-    construct(newValue);
+  /* implicit */ Optional(const Value& newValue) noexcept(
+      std::is_nothrow_copy_constructible<Value>::value) {
+    storage_.construct(newValue);
   }
 
-  ~Optional() {
-    clear();
+  template <typename... Args>
+  explicit Optional(in_place_t, Args&&... args) noexcept(
+      std::is_nothrow_constructible<Value, Args...>::value) {
+    storage_.construct(std::forward<Args>(args)...);
   }
 
   void assign(const None&) {
@@ -131,11 +138,13 @@ class Optional : boost::totally_ordered<Optional<Value>,
   }
 
   void assign(Optional&& src) {
-    if (src.hasValue()) {
-      assign(std::move(src.value()));
-      src.clear();
-    } else {
-      clear();
+    if (this != &src) {
+      if (src.hasValue()) {
+        assign(std::move(src.value()));
+        src.clear();
+      } else {
+        clear();
+      }
     }
   }
 
@@ -149,127 +158,211 @@ class Optional : boost::totally_ordered<Optional<Value>,
 
   void assign(Value&& newValue) {
     if (hasValue()) {
-      value_ = std::move(newValue);
+      *storage_.value_pointer() = std::move(newValue);
     } else {
-      construct(std::move(newValue));
+      storage_.construct(std::move(newValue));
     }
   }
 
   void assign(const Value& newValue) {
     if (hasValue()) {
-      value_ = newValue;
+      *storage_.value_pointer() = newValue;
     } else {
-      construct(newValue);
+      storage_.construct(newValue);
     }
   }
 
-  template<class Arg>
+  template <class Arg>
   Optional& operator=(Arg&& arg) {
     assign(std::forward<Arg>(arg));
     return *this;
   }
 
-  Optional& operator=(Optional &&other) {
+  Optional& operator=(Optional&& other) noexcept(
+      std::is_nothrow_move_assignable<Value>::value) {
     assign(std::move(other));
     return *this;
   }
 
-  Optional& operator=(const Optional &other) {
+  Optional& operator=(const Optional& other) noexcept(
+      std::is_nothrow_copy_assignable<Value>::value) {
     assign(other);
     return *this;
   }
 
-  bool operator<(const Optional& other) const {
-    if (hasValue() != other.hasValue()) {
-      return hasValue() < other.hasValue();
-    }
-    if (hasValue()) {
-      return value() < other.value();
-    }
-    return false; // both empty
+  template <class... Args>
+  void emplace(Args&&... args) {
+    clear();
+    storage_.construct(std::forward<Args>(args)...);
   }
 
-  bool operator<(const Value& other) const {
-    return !hasValue() || value() < other;
+  void clear() {
+    storage_.clear();
   }
 
-  bool operator==(const Optional& other) const {
-    if (hasValue()) {
-      return other.hasValue() && value() == other.value();
-    } else {
-      return !other.hasValue();
-    }
+  const Value& value() const & {
+    require_value();
+    return *storage_.value_pointer();
   }
 
-  bool operator==(const Value& other) const {
-    return hasValue() && value() == other;
+  Value& value() & {
+    require_value();
+    return *storage_.value_pointer();
   }
 
-  template<class... Args>
-  void emplace(Args&&... args) {
-    clear();
-    construct(std::forward<Args>(args)...);
+  Value&& value() && {
+    require_value();
+    return std::move(*storage_.value_pointer());
   }
 
-  void clear() {
-    if (hasValue()) {
-      hasValue_ = false;
-      value_.~Value();
-    }
+  const Value&& value() const && {
+    require_value();
+    return std::move(*storage_.value_pointer());
   }
 
-  const Value& value() const {
-    assert(hasValue());
-    return value_;
+  const Value* get_pointer() const & {
+    return storage_.value_pointer();
+  }
+  Value* get_pointer() & {
+    return storage_.value_pointer();
   }
+  Value* get_pointer() && = delete;
 
-  Value& value() {
-    assert(hasValue());
-    return value_;
+  bool hasValue() const {
+    return storage_.hasValue();
   }
 
-  bool hasValue() const { return hasValue_; }
+  explicit operator bool() const {
+    return hasValue();
+  }
 
-  /* safe bool idiom */
-  operator bool_type() const {
-    return hasValue() ? &Optional::truthy : nullptr;
+  const Value& operator*() const & {
+    return value();
+  }
+  Value& operator*() & {
+    return value();
+  }
+  const Value&& operator*() const && {
+    return std::move(value());
+  }
+  Value&& operator*() && {
+    return std::move(value());
+  }
+
+  const Value* operator->() const {
+    return &value();
+  }
+  Value* operator->() {
+    return &value();
   }
 
-  const Value& operator*() const { return value(); }
-        Value& operator*()       { return value(); }
+  // Return a copy of the value if set, or a given default if not.
+  template <class U>
+  Value value_or(U&& dflt) const & {
+    if (storage_.hasValue()) {
+      return *storage_.value_pointer();
+    }
+
+    return std::forward<U>(dflt);
+  }
 
-  const Value* operator->() const { return &value(); }
-        Value* operator->()       { return &value(); }
+  template <class U>
+  Value value_or(U&& dflt) && {
+    if (storage_.hasValue()) {
+      return std::move(*storage_.value_pointer());
+    }
+
+    return std::forward<U>(dflt);
+  }
 
  private:
-  template<class... Args>
-  void construct(Args&&... args) {
-    const void* ptr = &value_;
-    // for supporting const types
-    new(const_cast<void*>(ptr)) Value(std::forward<Args>(args)...);
-    hasValue_ = true;
+  void require_value() const {
+    if (!storage_.hasValue()) {
+      detail::throw_optional_empty_exception();
+    }
   }
 
-  // uninitialized
-  union { Value value_; };
-  bool hasValue_;
-};
+  struct StorageTriviallyDestructible {
+   protected:
+    bool hasValue_;
+    typename std::aligned_storage<sizeof(Value), alignof(Value)>::type
+        value_[1];
 
-#if defined(__GNUC__) && !defined(__clang__)
-#pragma GCC diagnostic pop
-#endif
+   public:
+    StorageTriviallyDestructible() : hasValue_{false} {}
+    void clear() {
+      hasValue_ = false;
+    }
+  };
+
+  struct StorageNonTriviallyDestructible {
+   protected:
+    bool hasValue_;
+    typename std::aligned_storage<sizeof(Value), alignof(Value)>::type
+        value_[1];
+
+   public:
+    StorageNonTriviallyDestructible() : hasValue_{false} {}
+    ~StorageNonTriviallyDestructible() {
+      clear();
+    }
+
+    void clear() {
+      if (hasValue_) {
+        hasValue_ = false;
+        launder(reinterpret_cast<Value*>(value_))->~Value();
+      }
+    }
+  };
+
+  struct Storage : std::conditional<
+                       std::is_trivially_destructible<Value>::value,
+                       StorageTriviallyDestructible,
+                       StorageNonTriviallyDestructible>::type {
+    bool hasValue() const {
+      return this->hasValue_;
+    }
+
+    Value* value_pointer() {
+      if (this->hasValue_) {
+        return launder(reinterpret_cast<Value*>(this->value_));
+      }
+      return nullptr;
+    }
 
-template<class T>
+    Value const* value_pointer() const {
+      if (this->hasValue_) {
+        return launder(reinterpret_cast<Value const*>(this->value_));
+      }
+      return nullptr;
+    }
+
+    template <class... Args>
+    void construct(Args&&... args) {
+      new (raw_pointer()) Value(std::forward<Args>(args)...);
+      this->hasValue_ = true;
+    }
+
+   private:
+    void* raw_pointer() {
+      return static_cast<void*>(this->value_);
+    }
+  };
+
+  Storage storage_;
+};
+
+template <class T>
 const T* get_pointer(const Optional<T>& opt) {
-  return opt ? &opt.value() : nullptr;
+  return opt.get_pointer();
 }
 
-template<class T>
+template <class T>
 T* get_pointer(Optional<T>& opt) {
-  return opt ? &opt.value() : nullptr;
+  return opt.get_pointer();
 }
 
-template<class T>
+template <class T>
 void swap(Optional<T>& a, Optional<T>& b) {
   if (a.hasValue() && b.hasValue()) {
     // both full
@@ -280,12 +373,107 @@ void swap(Optional<T>& a, Optional<T>& b) {
   }
 }
 
-template<class T,
-         class Opt = Optional<typename std::decay<T>::type>>
+template <class T, class Opt = Optional<typename std::decay<T>::type>>
 Opt make_optional(T&& v) {
   return Opt(std::forward<T>(v));
 }
 
+///////////////////////////////////////////////////////////////////////////////
+// Comparisons.
+
+template <class U, class V>
+bool operator==(const Optional<U>& a, const V& b) {
+  return a.hasValue() && a.value() == b;
+}
+
+template <class U, class V>
+bool operator!=(const Optional<U>& a, const V& b) {
+  return !(a == b);
+}
+
+template <class U, class V>
+bool operator==(const U& a, const Optional<V>& b) {
+  return b.hasValue() && b.value() == a;
+}
+
+template <class U, class V>
+bool operator!=(const U& a, const Optional<V>& b) {
+  return !(a == b);
+}
+
+template <class U, class V>
+bool operator==(const Optional<U>& a, const Optional<V>& b) {
+  if (a.hasValue() != b.hasValue()) {
+    return false;
+  }
+  if (a.hasValue()) {
+    return a.value() == b.value();
+  }
+  return true;
+}
+
+template <class U, class V>
+bool operator!=(const Optional<U>& a, const Optional<V>& b) {
+  return !(a == b);
+}
+
+template <class U, class V>
+bool operator<(const Optional<U>& a, const Optional<V>& b) {
+  if (a.hasValue() != b.hasValue()) {
+    return a.hasValue() < b.hasValue();
+  }
+  if (a.hasValue()) {
+    return a.value() < b.value();
+  }
+  return false;
+}
+
+template <class U, class V>
+bool operator>(const Optional<U>& a, const Optional<V>& b) {
+  return b < a;
+}
+
+template <class U, class V>
+bool operator<=(const Optional<U>& a, const Optional<V>& b) {
+  return !(b < a);
+}
+
+template <class U, class V>
+bool operator>=(const Optional<U>& a, const Optional<V>& b) {
+  return !(a < b);
+}
+
+// Suppress comparability of Optional<T> with T, despite implicit conversion.
+template <class V>
+bool operator<(const Optional<V>&, const V& other) = delete;
+template <class V>
+bool operator<=(const Optional<V>&, const V& other) = delete;
+template <class V>
+bool operator>=(const Optional<V>&, const V& other) = delete;
+template <class V>
+bool operator>(const Optional<V>&, const V& other) = delete;
+template <class V>
+bool operator<(const V& other, const Optional<V>&) = delete;
+template <class V>
+bool operator<=(const V& other, const Optional<V>&) = delete;
+template <class V>
+bool operator>=(const V& other, const Optional<V>&) = delete;
+template <class V>
+bool operator>(const V& other, const Optional<V>&) = delete;
+
+///////////////////////////////////////////////////////////////////////////////
+
 } // namespace folly
 
-#endif//FOLLY_OPTIONAL_H_
+// Allow usage of Optional<T> in std::unordered_map and std::unordered_set
+FOLLY_NAMESPACE_STD_BEGIN
+template <class T>
+struct hash<folly::Optional<T>> {
+  size_t operator()(folly::Optional<T> const& obj) const {
+    if (!obj.hasValue()) {
+      return 0;
+    }
+    return hash<typename remove_const<T>::type>()(*obj);
+  }
+};
+FOLLY_NAMESPACE_STD_END