X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=folly%2FOptional.h;h=5350b2ee5e44d69c55868c0a96e2e24d286a16fb;hb=9b2f7afe192834fdc4abc5687abc072bede25cd6;hp=3ff4c67f107f93f3d91188a8304eefff511c9c25;hpb=9faada6d332385cf3f3fd60daf8d7259523cb742;p=folly.git

diff --git a/folly/Optional.h b/folly/Optional.h
index 3ff4c67f..5350b2ee 100644
--- a/folly/Optional.h
+++ b/folly/Optional.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2014 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,
@@ -54,13 +53,13 @@
  *    cout << *v << endl;
  *  }
  */
-#include <cassert>
 #include <cstddef>
+#include <functional>
+#include <new>
+#include <stdexcept>
 #include <type_traits>
 #include <utility>
 
-#include <boost/operators.hpp>
-
 #include <folly/Portability.h>
 
 namespace folly {
@@ -71,25 +70,23 @@ 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__
+class OptionalEmptyException : public std::runtime_error {
+ public:
+  OptionalEmptyException()
+      : std::runtime_error("Empty Optional cannot be unwrapped") {}
+};
 
 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()
-    : hasValue_(false) {
+  Optional() noexcept {
   }
 
   Optional(const Optional& src)
@@ -97,8 +94,6 @@ class Optional {
 
     if (src.hasValue()) {
       construct(src.value());
-    } else {
-      hasValue_ = false;
     }
   }
 
@@ -108,13 +103,10 @@ class Optional {
     if (src.hasValue()) {
       construct(std::move(src.value()));
       src.clear();
-    } else {
-      hasValue_ = false;
     }
   }
 
-  /* implicit */ Optional(const None&) noexcept
-    : hasValue_(false) {
+  /* implicit */ Optional(const None&) noexcept {
   }
 
   /* implicit */ Optional(Value&& newValue)
@@ -127,10 +119,6 @@ class Optional {
     construct(newValue);
   }
 
-  ~Optional() noexcept {
-    clear();
-  }
-
   void assign(const None&) {
     clear();
   }
@@ -156,7 +144,7 @@ class Optional {
 
   void assign(Value&& newValue) {
     if (hasValue()) {
-      value_ = std::move(newValue);
+      storage_.value = std::move(newValue);
     } else {
       construct(std::move(newValue));
     }
@@ -164,7 +152,7 @@ class Optional {
 
   void assign(const Value& newValue) {
     if (hasValue()) {
-      value_ = newValue;
+      storage_.value = newValue;
     } else {
       construct(newValue);
     }
@@ -197,30 +185,47 @@ class Optional {
   }
 
   void clear() {
-    if (hasValue()) {
-      hasValue_ = false;
-      value_.~Value();
-    }
+    storage_.clear();
   }
 
-  const Value& value() const {
-    assert(hasValue());
-    return value_;
+  const Value& value() const& {
+    require_value();
+    return storage_.value;
   }
 
-  Value& value() {
-    assert(hasValue());
-    return value_;
+  Value& value() & {
+    require_value();
+    return storage_.value;
+  }
+
+  Value&& value() && {
+    require_value();
+    return std::move(storage_.value);
+  }
+
+  const Value&& value() const&& {
+    require_value();
+    return std::move(storage_.value);
+  }
+
+  const Value* get_pointer() const&  {
+    return storage_.hasValue ? &storage_.value : nullptr;
+  }
+  Value* get_pointer() & {
+    return storage_.hasValue ? &storage_.value : nullptr;
   }
+  Value* get_pointer() && = delete;
 
-  bool hasValue() const { return hasValue_; }
+  bool hasValue() const { return storage_.hasValue; }
 
   explicit operator bool() const {
     return hasValue();
   }
 
-  const Value& operator*() const { return value(); }
-        Value& operator*()       { return value(); }
+  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(); }
@@ -228,40 +233,103 @@ class Optional {
   // Return a copy of the value if set, or a given default if not.
   template <class U>
   Value value_or(U&& dflt) const& {
-    return hasValue_ ? value_ : std::forward<U>(dflt);
+    if (storage_.hasValue) {
+      return storage_.value;
+    }
+
+    return std::forward<U>(dflt);
   }
 
   template <class U>
   Value value_or(U&& dflt) && {
-    return hasValue_ ? std::move(value_) : std::forward<U>(dflt);
+    if (storage_.hasValue) {
+      return std::move(storage_.value);
+    }
+
+    return std::forward<U>(dflt);
   }
 
  private:
+  void require_value() const {
+    if (!storage_.hasValue) {
+      throw OptionalEmptyException();
+    }
+  }
+
   template<class... Args>
   void construct(Args&&... args) {
-    const void* ptr = &value_;
+    const void* ptr = &storage_.value;
     // for supporting const types
     new(const_cast<void*>(ptr)) Value(std::forward<Args>(args)...);
-    hasValue_ = true;
+    storage_.hasValue = true;
   }
 
-  // uninitialized
-  union { Value value_; };
-  bool hasValue_;
-};
+  struct StorageTriviallyDestructible {
+    // The union trick allows to initialize the Optional's memory,
+    // so that compiler/tools don't complain about uninitialized memory,
+    // without actually calling Value's default constructor.
+    // The rest of the implementation enforces that hasValue/value are
+    // synchronized.
+    union {
+      bool hasValue;
+      struct {
+        bool paddingForHasValue_[1];
+        Value value;
+      };
+    };
+
+    StorageTriviallyDestructible() : hasValue{false} {}
+
+    void clear() {
+      hasValue = false;
+    }
+  };
+
+  struct StorageNonTriviallyDestructible {
+    // See StorageTriviallyDestructible's union
+    union {
+      bool hasValue;
+      struct {
+        bool paddingForHasValue_[1];
+        Value value;
+      };
+    };
+
+    FOLLY_PUSH_WARNING
+    // These are both informational warnings, but they trigger rare enough
+    // that we've left them enabled.
+    FOLLY_MSVC_DISABLE_WARNING(4587) // constructor of .value is not called
+    FOLLY_MSVC_DISABLE_WARNING(4588) // destructor of .value is not called
+    StorageNonTriviallyDestructible() : hasValue{false} {}
+    ~StorageNonTriviallyDestructible() {
+      clear();
+    }
+    FOLLY_POP_WARNING
 
-#if defined(__GNUC__) && !defined(__clang__)
-#pragma GCC diagnostic pop
-#endif
+    void clear() {
+      if (hasValue) {
+        hasValue = false;
+        value.~Value();
+      }
+    }
+  };
+
+  using Storage =
+    typename std::conditional<std::is_trivially_destructible<Value>::value,
+                              StorageTriviallyDestructible,
+                              StorageNonTriviallyDestructible>::type;
+
+  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>
 T* get_pointer(Optional<T>& opt) {
-  return opt ? &opt.value() : nullptr;
+  return opt.get_pointer();
 }
 
 template<class T>
@@ -352,4 +420,15 @@ 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