Chris@47: // Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
Chris@47: // Licensed under the MIT License:
Chris@47: //
Chris@47: // Permission is hereby granted, free of charge, to any person obtaining a copy
Chris@47: // of this software and associated documentation files (the "Software"), to deal
Chris@47: // in the Software without restriction, including without limitation the rights
Chris@47: // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
Chris@47: // copies of the Software, and to permit persons to whom the Software is
Chris@47: // furnished to do so, subject to the following conditions:
Chris@47: //
Chris@47: // The above copyright notice and this permission notice shall be included in
Chris@47: // all copies or substantial portions of the Software.
Chris@47: //
Chris@47: // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
Chris@47: // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
Chris@47: // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
Chris@47: // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
Chris@47: // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
Chris@47: // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
Chris@47: // THE SOFTWARE.
Chris@47: 
Chris@47: #ifndef KJ_ONE_OF_H_
Chris@47: #define KJ_ONE_OF_H_
Chris@47: 
Chris@47: #if defined(__GNUC__) && !KJ_HEADER_WARNINGS
Chris@47: #pragma GCC system_header
Chris@47: #endif
Chris@47: 
Chris@47: #include "common.h"
Chris@47: 
Chris@47: namespace kj {
Chris@47: 
Chris@47: namespace _ {  // private
Chris@47: 
Chris@47: template <uint i, typename Key, typename First, typename... Rest>
Chris@47: struct TypeIndex_ { static constexpr uint value = TypeIndex_<i + 1, Key, Rest...>::value; };
Chris@47: template <uint i, typename Key, typename... Rest>
Chris@47: struct TypeIndex_<i, Key, Key, Rest...> { static constexpr uint value = i; };
Chris@47: 
Chris@47: }  // namespace _ (private)
Chris@47: 
Chris@47: template <typename... Variants>
Chris@47: class OneOf {
Chris@47:   template <typename Key>
Chris@47:   static inline constexpr uint typeIndex() { return _::TypeIndex_<1, Key, Variants...>::value; }
Chris@47:   // Get the 1-based index of Key within the type list Types.
Chris@47: 
Chris@47: public:
Chris@47:   inline OneOf(): tag(0) {}
Chris@47:   OneOf(const OneOf& other) { copyFrom(other); }
Chris@47:   OneOf(OneOf&& other) { moveFrom(other); }
Chris@47:   ~OneOf() { destroy(); }
Chris@47: 
Chris@47:   OneOf& operator=(const OneOf& other) { if (tag != 0) destroy(); copyFrom(other); return *this; }
Chris@47:   OneOf& operator=(OneOf&& other) { if (tag != 0) destroy(); moveFrom(other); return *this; }
Chris@47: 
Chris@47:   inline bool operator==(decltype(nullptr)) const { return tag == 0; }
Chris@47:   inline bool operator!=(decltype(nullptr)) const { return tag != 0; }
Chris@47: 
Chris@47:   template <typename T>
Chris@47:   bool is() const {
Chris@47:     return tag == typeIndex<T>();
Chris@47:   }
Chris@47: 
Chris@47:   template <typename T>
Chris@47:   T& get() {
Chris@47:     KJ_IREQUIRE(is<T>(), "Must check OneOf::is<T>() before calling get<T>().");
Chris@47:     return *reinterpret_cast<T*>(space);
Chris@47:   }
Chris@47:   template <typename T>
Chris@47:   const T& get() const {
Chris@47:     KJ_IREQUIRE(is<T>(), "Must check OneOf::is<T>() before calling get<T>().");
Chris@47:     return *reinterpret_cast<const T*>(space);
Chris@47:   }
Chris@47: 
Chris@47:   template <typename T, typename... Params>
Chris@47:   void init(Params&&... params) {
Chris@47:     if (tag != 0) destroy();
Chris@47:     ctor(*reinterpret_cast<T*>(space), kj::fwd<Params>(params)...);
Chris@47:     tag = typeIndex<T>();
Chris@47:   }
Chris@47: 
Chris@47: private:
Chris@47:   uint tag;
Chris@47: 
Chris@47:   static inline constexpr size_t maxSize(size_t a) {
Chris@47:     return a;
Chris@47:   }
Chris@47:   template <typename... Rest>
Chris@47:   static inline constexpr size_t maxSize(size_t a, size_t b, Rest... rest) {
Chris@47:     return maxSize(kj::max(a, b), rest...);
Chris@47:   }
Chris@47:   // Returns the maximum of all the parameters.
Chris@47:   // TODO(someday):  Generalize the above template and make it common.  I tried, but C++ decided to
Chris@47:   //   be difficult so I cut my losses.
Chris@47: 
Chris@47:   union {
Chris@47:     byte space[maxSize(sizeof(Variants)...)];
Chris@47: 
Chris@47:     void* forceAligned;
Chris@47:     // TODO(someday):  Use C++11 alignas() once we require GCC 4.8 / Clang 3.3.
Chris@47:   };
Chris@47: 
Chris@47:   template <typename... T>
Chris@47:   inline void doAll(T... t) {}
Chris@47: 
Chris@47:   template <typename T>
Chris@47:   inline bool destroyVariant() {
Chris@47:     if (tag == typeIndex<T>()) {
Chris@47:       tag = 0;
Chris@47:       dtor(*reinterpret_cast<T*>(space));
Chris@47:     }
Chris@47:     return false;
Chris@47:   }
Chris@47:   void destroy() {
Chris@47:     doAll(destroyVariant<Variants>()...);
Chris@47:   }
Chris@47: 
Chris@47:   template <typename T>
Chris@47:   inline bool copyVariantFrom(const OneOf& other) {
Chris@47:     if (other.is<T>()) {
Chris@47:       ctor(*reinterpret_cast<T*>(space), other.get<T>());
Chris@47:     }
Chris@47:     return false;
Chris@47:   }
Chris@47:   void copyFrom(const OneOf& other) {
Chris@47:     // Initialize as a copy of `other`.  Expects that `this` starts out uninitialized, so the tag
Chris@47:     // is invalid.
Chris@47:     tag = other.tag;
Chris@47:     doAll(copyVariantFrom<Variants>(other)...);
Chris@47:   }
Chris@47: 
Chris@47:   template <typename T>
Chris@47:   inline bool moveVariantFrom(OneOf& other) {
Chris@47:     if (other.is<T>()) {
Chris@47:       ctor(*reinterpret_cast<T*>(space), kj::mv(other.get<T>()));
Chris@47:     }
Chris@47:     return false;
Chris@47:   }
Chris@47:   void moveFrom(OneOf& other) {
Chris@47:     // Initialize as a copy of `other`.  Expects that `this` starts out uninitialized, so the tag
Chris@47:     // is invalid.
Chris@47:     tag = other.tag;
Chris@47:     doAll(moveVariantFrom<Variants>(other)...);
Chris@47:   }
Chris@47: };
Chris@47: 
Chris@47: }  // namespace kj
Chris@47: 
Chris@47: #endif  // KJ_ONE_OF_H_