jpayne@69: // Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
jpayne@69: // Licensed under the MIT License:
jpayne@69: //
jpayne@69: // Permission is hereby granted, free of charge, to any person obtaining a copy
jpayne@69: // of this software and associated documentation files (the "Software"), to deal
jpayne@69: // in the Software without restriction, including without limitation the rights
jpayne@69: // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
jpayne@69: // copies of the Software, and to permit persons to whom the Software is
jpayne@69: // furnished to do so, subject to the following conditions:
jpayne@69: //
jpayne@69: // The above copyright notice and this permission notice shall be included in
jpayne@69: // all copies or substantial portions of the Software.
jpayne@69: //
jpayne@69: // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
jpayne@69: // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
jpayne@69: // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
jpayne@69: // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
jpayne@69: // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
jpayne@69: // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
jpayne@69: // THE SOFTWARE.
jpayne@69: 
jpayne@69: #pragma once
jpayne@69: 
jpayne@69: #include "common.h"
jpayne@69: 
jpayne@69: KJ_BEGIN_HEADER
jpayne@69: 
jpayne@69: namespace kj {
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: inline constexpr bool _kj_internal_isPolymorphic(T*) {
jpayne@69:   // If you get a compiler error here complaining that T is incomplete, it's because you are trying
jpayne@69:   // to use kj::Own<T> with a type that has only been forward-declared. Since KJ doesn't know if
jpayne@69:   // the type might be involved in inheritance (especially multiple inheritance), it doesn't know
jpayne@69:   // how to correctly call the disposer to destroy the type, since the object's true memory address
jpayne@69:   // may differ from the address used to point to a superclass.
jpayne@69:   //
jpayne@69:   // However, if you know for sure that T is NOT polymorphic (i.e. it doesn't have a vtable and
jpayne@69:   // isn't involved in inheritance), then you can use KJ_DECLARE_NON_POLYMORPHIC(T) to declare this
jpayne@69:   // to KJ without actually completing the type. Place this macro invocation either in the global
jpayne@69:   // scope, or in the same namespace as T is defined.
jpayne@69:   return __is_polymorphic(T);
jpayne@69: }
jpayne@69: 
jpayne@69: #define KJ_DECLARE_NON_POLYMORPHIC(...) \
jpayne@69:   inline constexpr bool _kj_internal_isPolymorphic(__VA_ARGS__*) { \
jpayne@69:     return false; \
jpayne@69:   }
jpayne@69: // If you want to use kj::Own<T> for an incomplete type T that you know is not polymorphic, then
jpayne@69: // write `KJ_DECLARE_NON_POLYMORPHIC(T)` either at the global scope or in the same namespace as
jpayne@69: // T is declared.
jpayne@69: //
jpayne@69: // This also works for templates, e.g.:
jpayne@69: //
jpayne@69: //     template <typename X, typename Y>
jpayne@69: //     struct MyType;
jpayne@69: //     template <typename X, typename Y>
jpayne@69: //     KJ_DECLARE_NON_POLYMORPHIC(MyType<X, Y>)
jpayne@69: 
jpayne@69: namespace _ {  // private
jpayne@69: 
jpayne@69: template <typename T> struct RefOrVoid_ { typedef T& Type; };
jpayne@69: template <> struct RefOrVoid_<void> { typedef void Type; };
jpayne@69: template <> struct RefOrVoid_<const void> { typedef void Type; };
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: using RefOrVoid = typename RefOrVoid_<T>::Type;
jpayne@69: // Evaluates to T&, unless T is `void`, in which case evaluates to `void`.
jpayne@69: //
jpayne@69: // This is a hack needed to avoid defining Own<void> as a totally separate class.
jpayne@69: 
jpayne@69: template <typename T, bool isPolymorphic = _kj_internal_isPolymorphic((T*)nullptr)>
jpayne@69: struct CastToVoid_;
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: struct CastToVoid_<T, false> {
jpayne@69:   static void* apply(T* ptr) {
jpayne@69:     return static_cast<void*>(ptr);
jpayne@69:   }
jpayne@69:   static const void* applyConst(T* ptr) {
jpayne@69:     const T* cptr = ptr;
jpayne@69:     return static_cast<const void*>(cptr);
jpayne@69:   }
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: struct CastToVoid_<T, true> {
jpayne@69:   static void* apply(T* ptr) {
jpayne@69:     return dynamic_cast<void*>(ptr);
jpayne@69:   }
jpayne@69:   static const void* applyConst(T* ptr) {
jpayne@69:     const T* cptr = ptr;
jpayne@69:     return dynamic_cast<const void*>(cptr);
jpayne@69:   }
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: void* castToVoid(T* ptr) {
jpayne@69:   return CastToVoid_<T>::apply(ptr);
jpayne@69: }
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: const void* castToConstVoid(T* ptr) {
jpayne@69:   return CastToVoid_<T>::applyConst(ptr);
jpayne@69: }
jpayne@69: 
jpayne@69: }  // namespace _ (private)
jpayne@69: 
jpayne@69: // =======================================================================================
jpayne@69: // Disposer -- Implementation details.
jpayne@69: 
jpayne@69: class Disposer {
jpayne@69:   // Abstract interface for a thing that "disposes" of objects, where "disposing" usually means
jpayne@69:   // calling the destructor followed by freeing the underlying memory.  `Own<T>` encapsulates an
jpayne@69:   // object pointer with corresponding Disposer.
jpayne@69:   //
jpayne@69:   // Few developers will ever touch this interface.  It is primarily useful for those implementing
jpayne@69:   // custom memory allocators.
jpayne@69: 
jpayne@69: protected:
jpayne@69:   // Do not declare a destructor, as doing so will force a global initializer for each HeapDisposer
jpayne@69:   // instance.  Eww!
jpayne@69: 
jpayne@69:   virtual void disposeImpl(void* pointer) const = 0;
jpayne@69:   // Disposes of the object, given a pointer to the beginning of the object.  If the object is
jpayne@69:   // polymorphic, this pointer is determined by dynamic_cast<void*>().  For non-polymorphic types,
jpayne@69:   // Own<T> does not allow any casting, so the pointer exactly matches the original one given to
jpayne@69:   // Own<T>.
jpayne@69: 
jpayne@69: public:
jpayne@69: 
jpayne@69:   template <typename T>
jpayne@69:   void dispose(T* object) const;
jpayne@69:   // Helper wrapper around disposeImpl().
jpayne@69:   //
jpayne@69:   // If T is polymorphic, calls `disposeImpl(dynamic_cast<void*>(object))`, otherwise calls
jpayne@69:   // `disposeImpl(implicitCast<void*>(object))`.
jpayne@69:   //
jpayne@69:   // Callers must not call dispose() on the same pointer twice, even if the first call throws
jpayne@69:   // an exception.
jpayne@69: 
jpayne@69: private:
jpayne@69:   template <typename T, bool polymorphic = _kj_internal_isPolymorphic((T*)nullptr)>
jpayne@69:   struct Dispose_;
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: class DestructorOnlyDisposer: public Disposer {
jpayne@69:   // A disposer that merely calls the type's destructor and nothing else.
jpayne@69: 
jpayne@69: public:
jpayne@69:   static const DestructorOnlyDisposer instance;
jpayne@69: 
jpayne@69:   void disposeImpl(void* pointer) const override {
jpayne@69:     reinterpret_cast<T*>(pointer)->~T();
jpayne@69:   }
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: const DestructorOnlyDisposer<T> DestructorOnlyDisposer<T>::instance = DestructorOnlyDisposer<T>();
jpayne@69: 
jpayne@69: class NullDisposer: public Disposer {
jpayne@69:   // A disposer that does nothing.
jpayne@69: 
jpayne@69: public:
jpayne@69:   static const NullDisposer instance;
jpayne@69: 
jpayne@69:   void disposeImpl(void* pointer) const override {}
jpayne@69: };
jpayne@69: 
jpayne@69: // =======================================================================================
jpayne@69: // Own<T> -- An owned pointer.
jpayne@69: 
jpayne@69: template <typename T, typename StaticDisposer = decltype(nullptr)>
jpayne@69: class Own;
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: class Own<T, decltype(nullptr)> {
jpayne@69:   // A transferrable title to a T.  When an Own<T> goes out of scope, the object's Disposer is
jpayne@69:   // called to dispose of it.  An Own<T> can be efficiently passed by move, without relocating the
jpayne@69:   // underlying object; this transfers ownership.
jpayne@69:   //
jpayne@69:   // This is much like std::unique_ptr, except:
jpayne@69:   // - You cannot release().  An owned object is not necessarily allocated with new (see next
jpayne@69:   //   point), so it would be hard to use release() correctly.
jpayne@69:   // - The deleter is made polymorphic by virtual call rather than by template.  This is much
jpayne@69:   //   more powerful -- it allows the use of custom allocators, freelists, etc.  This could
jpayne@69:   //   _almost_ be accomplished with unique_ptr by forcing everyone to use something like
jpayne@69:   //   std::unique_ptr<T, kj::Deleter>, except that things get hairy in the presence of multiple
jpayne@69:   //   inheritance and upcasting, and anyway if you force everyone to use a custom deleter
jpayne@69:   //   then you've lost any benefit to interoperating with the "standard" unique_ptr.
jpayne@69: 
jpayne@69: public:
jpayne@69:   KJ_DISALLOW_COPY(Own);
jpayne@69:   inline Own(): disposer(nullptr), ptr(nullptr) {}
jpayne@69:   inline Own(Own&& other) noexcept
jpayne@69:       : disposer(other.disposer), ptr(other.ptr) { other.ptr = nullptr; }
jpayne@69:   inline Own(Own<RemoveConstOrDisable<T>>&& other) noexcept
jpayne@69:       : disposer(other.disposer), ptr(other.ptr) { other.ptr = nullptr; }
jpayne@69:   template <typename U, typename = EnableIf<canConvert<U*, T*>()>>
jpayne@69:   inline Own(Own<U>&& other) noexcept
jpayne@69:       : disposer(other.disposer), ptr(cast(other.ptr)) {
jpayne@69:     other.ptr = nullptr;
jpayne@69:   }
jpayne@69:   template <typename U, typename StaticDisposer, typename = EnableIf<canConvert<U*, T*>()>>
jpayne@69:   inline Own(Own<U, StaticDisposer>&& other) noexcept;
jpayne@69:   // Convert statically-disposed Own to dynamically-disposed Own.
jpayne@69:   inline Own(T* ptr, const Disposer& disposer) noexcept: disposer(&disposer), ptr(ptr) {}
jpayne@69: 
jpayne@69:   ~Own() noexcept(false) { dispose(); }
jpayne@69: 
jpayne@69:   inline Own& operator=(Own&& other) {
jpayne@69:     // Move-assignnment operator.
jpayne@69: 
jpayne@69:     // Careful, this might own `other`.  Therefore we have to transfer the pointers first, then
jpayne@69:     // dispose.
jpayne@69:     const Disposer* disposerCopy = disposer;
jpayne@69:     T* ptrCopy = ptr;
jpayne@69:     disposer = other.disposer;
jpayne@69:     ptr = other.ptr;
jpayne@69:     other.ptr = nullptr;
jpayne@69:     if (ptrCopy != nullptr) {
jpayne@69:       disposerCopy->dispose(const_cast<RemoveConst<T>*>(ptrCopy));
jpayne@69:     }
jpayne@69:     return *this;
jpayne@69:   }
jpayne@69: 
jpayne@69:   inline Own& operator=(decltype(nullptr)) {
jpayne@69:     dispose();
jpayne@69:     return *this;
jpayne@69:   }
jpayne@69: 
jpayne@69:   template <typename... Attachments>
jpayne@69:   Own<T> attach(Attachments&&... attachments) KJ_WARN_UNUSED_RESULT;
jpayne@69:   // Returns an Own<T> which points to the same object but which also ensures that all values
jpayne@69:   // passed to `attachments` remain alive until after this object is destroyed. Normally
jpayne@69:   // `attachments` are other Own<?>s pointing to objects that this one depends on.
jpayne@69:   //
jpayne@69:   // Note that attachments will eventually be destroyed in the order they are listed. Hence,
jpayne@69:   // foo.attach(bar, baz) is equivalent to (but more efficient than) foo.attach(bar).attach(baz).
jpayne@69: 
jpayne@69:   template <typename U>
jpayne@69:   Own<U> downcast() {
jpayne@69:     // Downcast the pointer to Own<U>, destroying the original pointer.  If this pointer does not
jpayne@69:     // actually point at an instance of U, the results are undefined (throws an exception in debug
jpayne@69:     // mode if RTTI is enabled, otherwise you're on your own).
jpayne@69: 
jpayne@69:     Own<U> result;
jpayne@69:     if (ptr != nullptr) {
jpayne@69:       result.ptr = &kj::downcast<U>(*ptr);
jpayne@69:       result.disposer = disposer;
jpayne@69:       ptr = nullptr;
jpayne@69:     }
jpayne@69:     return result;
jpayne@69:   }
jpayne@69: 
jpayne@69: #define NULLCHECK KJ_IREQUIRE(ptr != nullptr, "null Own<> dereference")
jpayne@69:   inline T* operator->() { NULLCHECK; return ptr; }
jpayne@69:   inline const T* operator->() const { NULLCHECK; return ptr; }
jpayne@69:   inline _::RefOrVoid<T> operator*() { NULLCHECK; return *ptr; }
jpayne@69:   inline _::RefOrVoid<const T> operator*() const { NULLCHECK; return *ptr; }
jpayne@69: #undef NULLCHECK
jpayne@69:   inline T* get() { return ptr; }
jpayne@69:   inline const T* get() const { return ptr; }
jpayne@69:   inline operator T*() { return ptr; }
jpayne@69:   inline operator const T*() const { return ptr; }
jpayne@69: 
jpayne@69: private:
jpayne@69:   const Disposer* disposer;  // Only valid if ptr != nullptr.
jpayne@69:   T* ptr;
jpayne@69: 
jpayne@69:   inline explicit Own(decltype(nullptr)): disposer(nullptr), ptr(nullptr) {}
jpayne@69: 
jpayne@69:   inline bool operator==(decltype(nullptr)) { return ptr == nullptr; }
jpayne@69:   inline bool operator!=(decltype(nullptr)) { return ptr != nullptr; }
jpayne@69:   // Only called by Maybe<Own<T>>.
jpayne@69: 
jpayne@69:   inline void dispose() {
jpayne@69:     // Make sure that if an exception is thrown, we are left with a null ptr, so we won't possibly
jpayne@69:     // dispose again.
jpayne@69:     T* ptrCopy = ptr;
jpayne@69:     if (ptrCopy != nullptr) {
jpayne@69:       ptr = nullptr;
jpayne@69:       disposer->dispose(const_cast<RemoveConst<T>*>(ptrCopy));
jpayne@69:     }
jpayne@69:   }
jpayne@69: 
jpayne@69:   template <typename U>
jpayne@69:   static inline T* cast(U* ptr) {
jpayne@69:     static_assert(_kj_internal_isPolymorphic((T*)nullptr),
jpayne@69:         "Casting owned pointers requires that the target type is polymorphic.");
jpayne@69:     return ptr;
jpayne@69:   }
jpayne@69: 
jpayne@69:   template <typename, typename>
jpayne@69:   friend class Own;
jpayne@69:   friend class Maybe<Own<T>>;
jpayne@69: };
jpayne@69: 
jpayne@69: template <>
jpayne@69: template <typename U>
jpayne@69: inline void* Own<void>::cast(U* ptr) {
jpayne@69:   return _::castToVoid(ptr);
jpayne@69: }
jpayne@69: 
jpayne@69: template <>
jpayne@69: template <typename U>
jpayne@69: inline const void* Own<const void>::cast(U* ptr) {
jpayne@69:   return _::castToConstVoid(ptr);
jpayne@69: }
jpayne@69: 
jpayne@69: template <typename T, typename StaticDisposer>
jpayne@69: class Own {
jpayne@69:   // If a `StaticDisposer` is specified (which is not the norm), then the object will be deleted
jpayne@69:   // by calling StaticDisposer::dispose(pointer). The pointer passed to `dispose()` could be a
jpayne@69:   // superclass of `T`, if the pointer has been upcast.
jpayne@69:   //
jpayne@69:   // This type can be useful for micro-optimization, if you've found that you are doing excessive
jpayne@69:   // heap allocations to the point where the virtual call on destruction is costing non-negligible
jpayne@69:   // resources. You should avoid this unless you have a specific need, because it precludes a lot
jpayne@69:   // of power.
jpayne@69: 
jpayne@69: public:
jpayne@69:   KJ_DISALLOW_COPY(Own);
jpayne@69:   inline Own(): ptr(nullptr) {}
jpayne@69:   inline Own(Own&& other) noexcept
jpayne@69:       : ptr(other.ptr) { other.ptr = nullptr; }
jpayne@69:   inline Own(Own<RemoveConstOrDisable<T>, StaticDisposer>&& other) noexcept
jpayne@69:       : ptr(other.ptr) { other.ptr = nullptr; }
jpayne@69:   template <typename U, typename = EnableIf<canConvert<U*, T*>()>>
jpayne@69:   inline Own(Own<U, StaticDisposer>&& other) noexcept
jpayne@69:       : ptr(cast(other.ptr)) {
jpayne@69:     other.ptr = nullptr;
jpayne@69:   }
jpayne@69:   inline explicit Own(T* ptr) noexcept: ptr(ptr) {}
jpayne@69: 
jpayne@69:   ~Own() noexcept(false) { dispose(); }
jpayne@69: 
jpayne@69:   inline Own& operator=(Own&& other) {
jpayne@69:     // Move-assignnment operator.
jpayne@69: 
jpayne@69:     // Careful, this might own `other`.  Therefore we have to transfer the pointers first, then
jpayne@69:     // dispose.
jpayne@69:     T* ptrCopy = ptr;
jpayne@69:     ptr = other.ptr;
jpayne@69:     other.ptr = nullptr;
jpayne@69:     if (ptrCopy != nullptr) {
jpayne@69:       StaticDisposer::dispose(ptrCopy);
jpayne@69:     }
jpayne@69:     return *this;
jpayne@69:   }
jpayne@69: 
jpayne@69:   inline Own& operator=(decltype(nullptr)) {
jpayne@69:     dispose();
jpayne@69:     return *this;
jpayne@69:   }
jpayne@69: 
jpayne@69:   template <typename U>
jpayne@69:   Own<U, StaticDisposer> downcast() {
jpayne@69:     // Downcast the pointer to Own<U>, destroying the original pointer.  If this pointer does not
jpayne@69:     // actually point at an instance of U, the results are undefined (throws an exception in debug
jpayne@69:     // mode if RTTI is enabled, otherwise you're on your own).
jpayne@69: 
jpayne@69:     Own<U, StaticDisposer> result;
jpayne@69:     if (ptr != nullptr) {
jpayne@69:       result.ptr = &kj::downcast<U>(*ptr);
jpayne@69:       ptr = nullptr;
jpayne@69:     }
jpayne@69:     return result;
jpayne@69:   }
jpayne@69: 
jpayne@69: #define NULLCHECK KJ_IREQUIRE(ptr != nullptr, "null Own<> dereference")
jpayne@69:   inline T* operator->() { NULLCHECK; return ptr; }
jpayne@69:   inline const T* operator->() const { NULLCHECK; return ptr; }
jpayne@69:   inline _::RefOrVoid<T> operator*() { NULLCHECK; return *ptr; }
jpayne@69:   inline _::RefOrVoid<const T> operator*() const { NULLCHECK; return *ptr; }
jpayne@69: #undef NULLCHECK
jpayne@69:   inline T* get() { return ptr; }
jpayne@69:   inline const T* get() const { return ptr; }
jpayne@69:   inline operator T*() { return ptr; }
jpayne@69:   inline operator const T*() const { return ptr; }
jpayne@69: 
jpayne@69: private:
jpayne@69:   T* ptr;
jpayne@69: 
jpayne@69:   inline explicit Own(decltype(nullptr)): ptr(nullptr) {}
jpayne@69: 
jpayne@69:   inline bool operator==(decltype(nullptr)) { return ptr == nullptr; }
jpayne@69:   inline bool operator!=(decltype(nullptr)) { return ptr != nullptr; }
jpayne@69:   // Only called by Maybe<Own<T>>.
jpayne@69: 
jpayne@69:   inline void dispose() {
jpayne@69:     // Make sure that if an exception is thrown, we are left with a null ptr, so we won't possibly
jpayne@69:     // dispose again.
jpayne@69:     T* ptrCopy = ptr;
jpayne@69:     if (ptrCopy != nullptr) {
jpayne@69:       ptr = nullptr;
jpayne@69:       StaticDisposer::dispose(ptrCopy);
jpayne@69:     }
jpayne@69:   }
jpayne@69: 
jpayne@69:   template <typename U>
jpayne@69:   static inline T* cast(U* ptr) {
jpayne@69:     return ptr;
jpayne@69:   }
jpayne@69: 
jpayne@69:   template <typename, typename>
jpayne@69:   friend class Own;
jpayne@69:   friend class Maybe<Own<T, StaticDisposer>>;
jpayne@69: };
jpayne@69: 
jpayne@69: namespace _ {  // private
jpayne@69: 
jpayne@69: template <typename T, typename D>
jpayne@69: class OwnOwn {
jpayne@69: public:
jpayne@69:   inline OwnOwn(Own<T, D>&& value) noexcept: value(kj::mv(value)) {}
jpayne@69: 
jpayne@69:   inline Own<T, D>& operator*() & { return value; }
jpayne@69:   inline const Own<T, D>& operator*() const & { return value; }
jpayne@69:   inline Own<T, D>&& operator*() && { return kj::mv(value); }
jpayne@69:   inline const Own<T, D>&& operator*() const && { return kj::mv(value); }
jpayne@69:   inline Own<T, D>* operator->() { return &value; }
jpayne@69:   inline const Own<T, D>* operator->() const { return &value; }
jpayne@69:   inline operator Own<T, D>*() { return value ? &value : nullptr; }
jpayne@69:   inline operator const Own<T, D>*() const { return value ? &value : nullptr; }
jpayne@69: 
jpayne@69: private:
jpayne@69:   Own<T, D> value;
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T, typename D>
jpayne@69: OwnOwn<T, D> readMaybe(Maybe<Own<T, D>>&& maybe) { return OwnOwn<T, D>(kj::mv(maybe.ptr)); }
jpayne@69: template <typename T, typename D>
jpayne@69: Own<T, D>* readMaybe(Maybe<Own<T, D>>& maybe) { return maybe.ptr ? &maybe.ptr : nullptr; }
jpayne@69: template <typename T, typename D>
jpayne@69: const Own<T, D>* readMaybe(const Maybe<Own<T, D>>& maybe) {
jpayne@69:   return maybe.ptr ? &maybe.ptr : nullptr;
jpayne@69: }
jpayne@69: 
jpayne@69: }  // namespace _ (private)
jpayne@69: 
jpayne@69: template <typename T, typename D>
jpayne@69: class Maybe<Own<T, D>> {
jpayne@69: public:
jpayne@69:   inline Maybe(): ptr(nullptr) {}
jpayne@69:   inline Maybe(Own<T, D>&& t) noexcept: ptr(kj::mv(t)) {}
jpayne@69:   inline Maybe(Maybe&& other) noexcept: ptr(kj::mv(other.ptr)) {}
jpayne@69: 
jpayne@69:   template <typename U>
jpayne@69:   inline Maybe(Maybe<Own<U, D>>&& other): ptr(mv(other.ptr)) {}
jpayne@69:   template <typename U>
jpayne@69:   inline Maybe(Own<U, D>&& other): ptr(mv(other)) {}
jpayne@69: 
jpayne@69:   inline Maybe(decltype(nullptr)) noexcept: ptr(nullptr) {}
jpayne@69: 
jpayne@69:   inline Own<T, D>& emplace(Own<T, D> value) {
jpayne@69:     // Assign the Maybe to the given value and return the content. This avoids the need to do a
jpayne@69:     // KJ_ASSERT_NONNULL() immediately after setting the Maybe just to read it back again.
jpayne@69:     ptr = kj::mv(value);
jpayne@69:     return ptr;
jpayne@69:   }
jpayne@69: 
jpayne@69:   template <typename U = T>
jpayne@69:   inline operator NoInfer<Maybe<U&>>() { return ptr.get(); }
jpayne@69:   template <typename U = T>
jpayne@69:   inline operator NoInfer<Maybe<const U&>>() const { return ptr.get(); }
jpayne@69:   // Implicit conversion to `Maybe<U&>`. The weird templating is to make sure that
jpayne@69:   // `Maybe<Own<void>>` can be instantiated with the compiler complaining about forming references
jpayne@69:   // to void -- the use of templates here will cause SFINAE to kick in and hide these, whereas if
jpayne@69:   // they are not templates then SFINAE isn't applied and so they are considered errors.
jpayne@69: 
jpayne@69:   inline Maybe& operator=(Maybe&& other) { ptr = kj::mv(other.ptr); return *this; }
jpayne@69: 
jpayne@69:   inline bool operator==(decltype(nullptr)) const { return ptr == nullptr; }
jpayne@69:   inline bool operator!=(decltype(nullptr)) const { return ptr != nullptr; }
jpayne@69: 
jpayne@69:   Own<T, D>& orDefault(Own<T, D>& defaultValue) {
jpayne@69:     if (ptr == nullptr) {
jpayne@69:       return defaultValue;
jpayne@69:     } else {
jpayne@69:       return ptr;
jpayne@69:     }
jpayne@69:   }
jpayne@69:   const Own<T, D>& orDefault(const Own<T, D>& defaultValue) const {
jpayne@69:     if (ptr == nullptr) {
jpayne@69:       return defaultValue;
jpayne@69:     } else {
jpayne@69:       return ptr;
jpayne@69:     }
jpayne@69:   }
jpayne@69: 
jpayne@69:   template <typename F,
jpayne@69:       typename Result = decltype(instance<bool>() ? instance<Own<T, D>>() : instance<F>()())>
jpayne@69:   Result orDefault(F&& lazyDefaultValue) && {
jpayne@69:     if (ptr == nullptr) {
jpayne@69:       return lazyDefaultValue();
jpayne@69:     } else {
jpayne@69:       return kj::mv(ptr);
jpayne@69:     }
jpayne@69:   }
jpayne@69: 
jpayne@69:   template <typename Func>
jpayne@69:   auto map(Func&& f) & -> Maybe<decltype(f(instance<Own<T, D>&>()))> {
jpayne@69:     if (ptr == nullptr) {
jpayne@69:       return nullptr;
jpayne@69:     } else {
jpayne@69:       return f(ptr);
jpayne@69:     }
jpayne@69:   }
jpayne@69: 
jpayne@69:   template <typename Func>
jpayne@69:   auto map(Func&& f) const & -> Maybe<decltype(f(instance<const Own<T, D>&>()))> {
jpayne@69:     if (ptr == nullptr) {
jpayne@69:       return nullptr;
jpayne@69:     } else {
jpayne@69:       return f(ptr);
jpayne@69:     }
jpayne@69:   }
jpayne@69: 
jpayne@69:   template <typename Func>
jpayne@69:   auto map(Func&& f) && -> Maybe<decltype(f(instance<Own<T, D>&&>()))> {
jpayne@69:     if (ptr == nullptr) {
jpayne@69:       return nullptr;
jpayne@69:     } else {
jpayne@69:       return f(kj::mv(ptr));
jpayne@69:     }
jpayne@69:   }
jpayne@69: 
jpayne@69:   template <typename Func>
jpayne@69:   auto map(Func&& f) const && -> Maybe<decltype(f(instance<const Own<T, D>&&>()))> {
jpayne@69:     if (ptr == nullptr) {
jpayne@69:       return nullptr;
jpayne@69:     } else {
jpayne@69:       return f(kj::mv(ptr));
jpayne@69:     }
jpayne@69:   }
jpayne@69: 
jpayne@69: private:
jpayne@69:   Own<T, D> ptr;
jpayne@69: 
jpayne@69:   template <typename U>
jpayne@69:   friend class Maybe;
jpayne@69:   template <typename U, typename D2>
jpayne@69:   friend _::OwnOwn<U, D2> _::readMaybe(Maybe<Own<U, D2>>&& maybe);
jpayne@69:   template <typename U, typename D2>
jpayne@69:   friend Own<U, D2>* _::readMaybe(Maybe<Own<U, D2>>& maybe);
jpayne@69:   template <typename U, typename D2>
jpayne@69:   friend const Own<U, D2>* _::readMaybe(const Maybe<Own<U, D2>>& maybe);
jpayne@69: };
jpayne@69: 
jpayne@69: namespace _ {  // private
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: class HeapDisposer final: public Disposer {
jpayne@69: public:
jpayne@69:   virtual void disposeImpl(void* pointer) const override { delete reinterpret_cast<T*>(pointer); }
jpayne@69: 
jpayne@69:   static const HeapDisposer instance;
jpayne@69: };
jpayne@69: 
jpayne@69: #if _MSC_VER && _MSC_VER < 1920 && !defined(__clang__)
jpayne@69: template <typename T>
jpayne@69: __declspec(selectany) const HeapDisposer<T> HeapDisposer<T>::instance = HeapDisposer<T>();
jpayne@69: // On MSVC 2017 we suddenly started seeing a linker error on one specific specialization of
jpayne@69: // `HeapDisposer::instance` when seemingly-unrelated code was modified. Explicitly specifying
jpayne@69: // `__declspec(selectany)` seems to fix it. But why? Shouldn't template members have `selectany`
jpayne@69: // behavior by default? We don't know. It works and we're moving on.
jpayne@69: #else
jpayne@69: template <typename T>
jpayne@69: const HeapDisposer<T> HeapDisposer<T>::instance = HeapDisposer<T>();
jpayne@69: #endif
jpayne@69: 
jpayne@69: #if KJ_CPP_STD >= 202002L
jpayne@69: template <typename T, void(*F)(T*)>
jpayne@69: class CustomDisposer: public Disposer {
jpayne@69: public:
jpayne@69:   void disposeImpl(void* pointer) const override {
jpayne@69:     (*F)(reinterpret_cast<T*>(pointer));
jpayne@69:   }
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T, void(*F)(T*)>
jpayne@69: static constexpr CustomDisposer<T, F> CUSTOM_DISPOSER_INSTANCE {};
jpayne@69: #else
jpayne@69: template <typename T, void(*F)(T*)>
jpayne@69: class CustomDisposer: public Disposer {
jpayne@69: public:
jpayne@69:   static const CustomDisposer instance;
jpayne@69: 
jpayne@69:   void disposeImpl(void* pointer) const override {
jpayne@69:     (*F)(reinterpret_cast<T*>(pointer));
jpayne@69:   }
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T, void(*F)(T*)>
jpayne@69: const CustomDisposer<T, F> CustomDisposer<T, F>::instance = CustomDisposer<T, F>();
jpayne@69: #endif
jpayne@69: 
jpayne@69: }  // namespace _ (private)
jpayne@69: 
jpayne@69: template <typename T, typename... Params>
jpayne@69: Own<T> heap(Params&&... params) {
jpayne@69:   // heap<T>(...) allocates a T on the heap, forwarding the parameters to its constructor.  The
jpayne@69:   // exact heap implementation is unspecified -- for now it is operator new, but you should not
jpayne@69:   // assume this.  (Since we know the object size at delete time, we could actually implement an
jpayne@69:   // allocator that is more efficient than operator new.)
jpayne@69: 
jpayne@69:   return Own<T>(new T(kj::fwd<Params>(params)...), _::HeapDisposer<T>::instance);
jpayne@69: }
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: Own<Decay<T>> heap(T&& orig) {
jpayne@69:   // Allocate a copy (or move) of the argument on the heap.
jpayne@69:   //
jpayne@69:   // The purpose of this overload is to allow you to omit the template parameter as there is only
jpayne@69:   // one argument and the purpose is to copy it.
jpayne@69: 
jpayne@69:   typedef Decay<T> T2;
jpayne@69:   return Own<T2>(new T2(kj::fwd<T>(orig)), _::HeapDisposer<T2>::instance);
jpayne@69: }
jpayne@69: 
jpayne@69: #if KJ_CPP_STD > 201402L
jpayne@69: #if KJ_CPP_STD < 202002L
jpayne@69: template <auto F, typename T>
jpayne@69: Own<T> disposeWith(T* ptr) {
jpayne@69:   // Associate a pre-allocated raw pointer with a corresponding disposal function.
jpayne@69:   // The first template parameter should be a function pointer e.g. disposeWith<freeInt>(new int(0)).
jpayne@69: 
jpayne@69:   return Own<T>(ptr, _::CustomDisposer<T, F>::instance);
jpayne@69: }
jpayne@69: #else
jpayne@69: template <auto F, typename T>
jpayne@69: Own<T> disposeWith(T* ptr) {
jpayne@69:   // Associate a pre-allocated raw pointer with a corresponding disposal function.
jpayne@69:   // The first template parameter should be a function pointer e.g. disposeWith<freeInt>(new int(0)).
jpayne@69: 
jpayne@69:   return Own<T>(ptr, _::CUSTOM_DISPOSER_INSTANCE<T, F>);
jpayne@69: }
jpayne@69: #endif
jpayne@69: #endif
jpayne@69: 
jpayne@69: template <typename T, typename... Attachments>
jpayne@69: Own<Decay<T>> attachVal(T&& value, Attachments&&... attachments);
jpayne@69: // Returns an Own<T> that takes ownership of `value` and `attachments`, and points to `value`.
jpayne@69: //
jpayne@69: // This is equivalent to heap(value).attach(attachments), but only does one allocation rather than
jpayne@69: // two.
jpayne@69: 
jpayne@69: template <typename T, typename... Attachments>
jpayne@69: Own<T> attachRef(T& value, Attachments&&... attachments);
jpayne@69: // Like attach() but `value` is not moved; the resulting Own<T> points to its existing location.
jpayne@69: // This is preferred if `value` is already owned by one of `attachments`.
jpayne@69: //
jpayne@69: // This is equivalent to Own<T>(&value, kj::NullDisposer::instance).attach(attachments), but
jpayne@69: // is easier to write and allocates slightly less memory.
jpayne@69: 
jpayne@69: // =======================================================================================
jpayne@69: // SpaceFor<T> -- assists in manual allocation
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: class SpaceFor {
jpayne@69:   // A class which has the same size and alignment as T but does not call its constructor or
jpayne@69:   // destructor automatically.  Instead, call construct() to construct a T in the space, which
jpayne@69:   // returns an Own<T> which will take care of calling T's destructor later.
jpayne@69: 
jpayne@69: public:
jpayne@69:   inline SpaceFor() {}
jpayne@69:   inline ~SpaceFor() {}
jpayne@69: 
jpayne@69:   template <typename... Params>
jpayne@69:   Own<T> construct(Params&&... params) {
jpayne@69:     ctor(value, kj::fwd<Params>(params)...);
jpayne@69:     return Own<T>(&value, DestructorOnlyDisposer<T>::instance);
jpayne@69:   }
jpayne@69: 
jpayne@69: private:
jpayne@69:   union {
jpayne@69:     T value;
jpayne@69:   };
jpayne@69: };
jpayne@69: 
jpayne@69: // =======================================================================================
jpayne@69: // Inline implementation details
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: struct Disposer::Dispose_<T, true> {
jpayne@69:   static void dispose(T* object, const Disposer& disposer) {
jpayne@69:     // Note that dynamic_cast<void*> does not require RTTI to be enabled, because the offset to
jpayne@69:     // the top of the object is in the vtable -- as it obviously needs to be to correctly implement
jpayne@69:     // operator delete.
jpayne@69:     disposer.disposeImpl(dynamic_cast<void*>(object));
jpayne@69:   }
jpayne@69: };
jpayne@69: template <typename T>
jpayne@69: struct Disposer::Dispose_<T, false> {
jpayne@69:   static void dispose(T* object, const Disposer& disposer) {
jpayne@69:     disposer.disposeImpl(static_cast<void*>(object));
jpayne@69:   }
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: void Disposer::dispose(T* object) const {
jpayne@69:   Dispose_<T>::dispose(object, *this);
jpayne@69: }
jpayne@69: 
jpayne@69: namespace _ {  // private
jpayne@69: 
jpayne@69: template <typename... T>
jpayne@69: struct OwnedBundle;
jpayne@69: 
jpayne@69: template <>
jpayne@69: struct OwnedBundle<> {};
jpayne@69: 
jpayne@69: template <typename First, typename... Rest>
jpayne@69: struct OwnedBundle<First, Rest...>: public OwnedBundle<Rest...> {
jpayne@69:   OwnedBundle(First&& first, Rest&&... rest)
jpayne@69:       : OwnedBundle<Rest...>(kj::fwd<Rest>(rest)...), first(kj::fwd<First>(first)) {}
jpayne@69: 
jpayne@69:   // Note that it's intentional that `first` is destroyed before `rest`. This way, doing
jpayne@69:   // ptr.attach(foo, bar, baz) is equivalent to ptr.attach(foo).attach(bar).attach(baz) in terms
jpayne@69:   // of destruction order (although the former does fewer allocations).
jpayne@69:   Decay<First> first;
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename... T>
jpayne@69: struct DisposableOwnedBundle final: public Disposer, public OwnedBundle<T...> {
jpayne@69:   DisposableOwnedBundle(T&&... values): OwnedBundle<T...>(kj::fwd<T>(values)...) {}
jpayne@69:   void disposeImpl(void* pointer) const override { delete this; }
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T, typename StaticDisposer>
jpayne@69: class StaticDisposerAdapter final: public Disposer {
jpayne@69:   // Adapts a static disposer to be called dynamically.
jpayne@69: public:
jpayne@69:   virtual void disposeImpl(void* pointer) const override {
jpayne@69:     StaticDisposer::dispose(reinterpret_cast<T*>(pointer));
jpayne@69:   }
jpayne@69: 
jpayne@69:   static const StaticDisposerAdapter instance;
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T, typename D>
jpayne@69: const StaticDisposerAdapter<T, D> StaticDisposerAdapter<T, D>::instance =
jpayne@69:     StaticDisposerAdapter<T, D>();
jpayne@69: 
jpayne@69: }  // namespace _ (private)
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: template <typename... Attachments>
jpayne@69: Own<T> Own<T>::attach(Attachments&&... attachments) {
jpayne@69:   T* ptrCopy = ptr;
jpayne@69: 
jpayne@69:   KJ_IREQUIRE(ptrCopy != nullptr, "cannot attach to null pointer");
jpayne@69: 
jpayne@69:   // HACK: If someone accidentally calls .attach() on a null pointer in opt mode, try our best to
jpayne@69:   //   accomplish reasonable behavior: We turn the pointer non-null but still invalid, so that the
jpayne@69:   //   disposer will still be called when the pointer goes out of scope.
jpayne@69:   if (ptrCopy == nullptr) ptrCopy = reinterpret_cast<T*>(1);
jpayne@69: 
jpayne@69:   auto bundle = new _::DisposableOwnedBundle<Own<T>, Attachments...>(
jpayne@69:       kj::mv(*this), kj::fwd<Attachments>(attachments)...);
jpayne@69:   return Own<T>(ptrCopy, *bundle);
jpayne@69: }
jpayne@69: 
jpayne@69: template <typename T, typename... Attachments>
jpayne@69: Own<T> attachRef(T& value, Attachments&&... attachments) {
jpayne@69:   auto bundle = new _::DisposableOwnedBundle<Attachments...>(kj::fwd<Attachments>(attachments)...);
jpayne@69:   return Own<T>(&value, *bundle);
jpayne@69: }
jpayne@69: 
jpayne@69: template <typename T, typename... Attachments>
jpayne@69: Own<Decay<T>> attachVal(T&& value, Attachments&&... attachments) {
jpayne@69:   auto bundle = new _::DisposableOwnedBundle<T, Attachments...>(
jpayne@69:       kj::fwd<T>(value), kj::fwd<Attachments>(attachments)...);
jpayne@69:   return Own<Decay<T>>(&bundle->first, *bundle);
jpayne@69: }
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: template <typename U, typename StaticDisposer, typename>
jpayne@69: inline Own<T>::Own(Own<U, StaticDisposer>&& other) noexcept
jpayne@69:     : ptr(cast(other.ptr)) {
jpayne@69:   if (_::castToVoid(other.ptr) != reinterpret_cast<void*>(other.ptr)) {
jpayne@69:     // Oh dangit, there's some sort of multiple inheritance going on and `StaticDisposerAdapter`
jpayne@69:     // won't actually work because it'll receive a pointer pointing to the top of the object, which
jpayne@69:     // isn't exactly the same as the `U*` pointer it wants. We have no choice but to allocate
jpayne@69:     // a dynamic disposer here.
jpayne@69:     disposer = new _::DisposableOwnedBundle<Own<U, StaticDisposer>>(kj::mv(other));
jpayne@69:   } else {
jpayne@69:     disposer = &_::StaticDisposerAdapter<U, StaticDisposer>::instance;
jpayne@69:     other.ptr = nullptr;
jpayne@69:   }
jpayne@69: }
jpayne@69: 
jpayne@69: }  // namespace kj
jpayne@69: 
jpayne@69: KJ_END_HEADER