diff osx/include/kj/memory.h @ 147:45360b968bf4

Cap'n Proto v0.6 + build for OSX

--- a/osx/include/kj/memory.h	Mon Mar 06 13:29:58 2017 +0000
+++ b/osx/include/kj/memory.h	Mon May 22 10:01:37 2017 +0100
@@ -1,404 +1,406 @@
-// Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
-// Licensed under the MIT License:
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in
-// all copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
-// THE SOFTWARE.
-
-#ifndef KJ_MEMORY_H_
-#define KJ_MEMORY_H_
-
-#if defined(__GNUC__) && !KJ_HEADER_WARNINGS
-#pragma GCC system_header
-#endif
-
-#include "common.h"
-
-namespace kj {
-
-// =======================================================================================
-// Disposer -- Implementation details.
-
-class Disposer {
-  // Abstract interface for a thing that "disposes" of objects, where "disposing" usually means
-  // calling the destructor followed by freeing the underlying memory.  `Own<T>` encapsulates an
-  // object pointer with corresponding Disposer.
-  //
-  // Few developers will ever touch this interface.  It is primarily useful for those implementing
-  // custom memory allocators.
-
-protected:
-  // Do not declare a destructor, as doing so will force a global initializer for each HeapDisposer
-  // instance.  Eww!
-
-  virtual void disposeImpl(void* pointer) const = 0;
-  // Disposes of the object, given a pointer to the beginning of the object.  If the object is
-  // polymorphic, this pointer is determined by dynamic_cast<void*>().  For non-polymorphic types,
-  // Own<T> does not allow any casting, so the pointer exactly matches the original one given to
-  // Own<T>.
-
-public:
-
-  template <typename T>
-  void dispose(T* object) const;
-  // Helper wrapper around disposeImpl().
-  //
-  // If T is polymorphic, calls `disposeImpl(dynamic_cast<void*>(object))`, otherwise calls
-  // `disposeImpl(implicitCast<void*>(object))`.
-  //
-  // Callers must not call dispose() on the same pointer twice, even if the first call throws
-  // an exception.
-
-private:
-  template <typename T, bool polymorphic = __is_polymorphic(T)>
-  struct Dispose_;
-};
-
-template <typename T>
-class DestructorOnlyDisposer: public Disposer {
-  // A disposer that merely calls the type's destructor and nothing else.
-
-public:
-  static const DestructorOnlyDisposer instance;
-
-  void disposeImpl(void* pointer) const override {
-    reinterpret_cast<T*>(pointer)->~T();
-  }
-};
-
-template <typename T>
-const DestructorOnlyDisposer<T> DestructorOnlyDisposer<T>::instance = DestructorOnlyDisposer<T>();
-
-class NullDisposer: public Disposer {
-  // A disposer that does nothing.
-
-public:
-  static const NullDisposer instance;
-
-  void disposeImpl(void* pointer) const override {}
-};
-
-// =======================================================================================
-// Own<T> -- An owned pointer.
-
-template <typename T>
-class Own {
-  // A transferrable title to a T.  When an Own<T> goes out of scope, the object's Disposer is
-  // called to dispose of it.  An Own<T> can be efficiently passed by move, without relocating the
-  // underlying object; this transfers ownership.
-  //
-  // This is much like std::unique_ptr, except:
-  // - You cannot release().  An owned object is not necessarily allocated with new (see next
-  //   point), so it would be hard to use release() correctly.
-  // - The deleter is made polymorphic by virtual call rather than by template.  This is much
-  //   more powerful -- it allows the use of custom allocators, freelists, etc.  This could
-  //   _almost_ be accomplished with unique_ptr by forcing everyone to use something like
-  //   std::unique_ptr<T, kj::Deleter>, except that things get hairy in the presence of multiple
-  //   inheritance and upcasting, and anyway if you force everyone to use a custom deleter
-  //   then you've lost any benefit to interoperating with the "standard" unique_ptr.
-
-public:
-  KJ_DISALLOW_COPY(Own);
-  inline Own(): disposer(nullptr), ptr(nullptr) {}
-  inline Own(Own&& other) noexcept
-      : disposer(other.disposer), ptr(other.ptr) { other.ptr = nullptr; }
-  inline Own(Own<RemoveConstOrDisable<T>>&& other) noexcept
-      : disposer(other.disposer), ptr(other.ptr) { other.ptr = nullptr; }
-  template <typename U, typename = EnableIf<canConvert<U*, T*>()>>
-  inline Own(Own<U>&& other) noexcept
-      : disposer(other.disposer), ptr(other.ptr) {
-    static_assert(__is_polymorphic(T),
-        "Casting owned pointers requires that the target type is polymorphic.");
-    other.ptr = nullptr;
-  }
-  inline Own(T* ptr, const Disposer& disposer) noexcept: disposer(&disposer), ptr(ptr) {}
-
-  ~Own() noexcept(false) { dispose(); }
-
-  inline Own& operator=(Own&& other) {
-    // Move-assingnment operator.
-
-    // Careful, this might own `other`.  Therefore we have to transfer the pointers first, then
-    // dispose.
-    const Disposer* disposerCopy = disposer;
-    T* ptrCopy = ptr;
-    disposer = other.disposer;
-    ptr = other.ptr;
-    other.ptr = nullptr;
-    if (ptrCopy != nullptr) {
-      disposerCopy->dispose(const_cast<RemoveConst<T>*>(ptrCopy));
-    }
-    return *this;
-  }
-
-  inline Own& operator=(decltype(nullptr)) {
-    dispose();
-    return *this;
-  }
-
-  template <typename U>
-  Own<U> downcast() {
-    // Downcast the pointer to Own<U>, destroying the original pointer.  If this pointer does not
-    // actually point at an instance of U, the results are undefined (throws an exception in debug
-    // mode if RTTI is enabled, otherwise you're on your own).
-
-    Own<U> result;
-    if (ptr != nullptr) {
-      result.ptr = &kj::downcast<U>(*ptr);
-      result.disposer = disposer;
-      ptr = nullptr;
-    }
-    return result;
-  }
-
-#define NULLCHECK KJ_IREQUIRE(ptr != nullptr, "null Own<> dereference")
-  inline T* operator->() { NULLCHECK; return ptr; }
-  inline const T* operator->() const { NULLCHECK; return ptr; }
-  inline T& operator*() { NULLCHECK; return *ptr; }
-  inline const T& operator*() const { NULLCHECK; return *ptr; }
-#undef NULLCHECK
-  inline T* get() { return ptr; }
-  inline const T* get() const { return ptr; }
-  inline operator T*() { return ptr; }
-  inline operator const T*() const { return ptr; }
-
-private:
-  const Disposer* disposer;  // Only valid if ptr != nullptr.
-  T* ptr;
-
-  inline explicit Own(decltype(nullptr)): disposer(nullptr), ptr(nullptr) {}
-
-  inline bool operator==(decltype(nullptr)) { return ptr == nullptr; }
-  inline bool operator!=(decltype(nullptr)) { return ptr != nullptr; }
-  // Only called by Maybe<Own<T>>.
-
-  inline void dispose() {
-    // Make sure that if an exception is thrown, we are left with a null ptr, so we won't possibly
-    // dispose again.
-    T* ptrCopy = ptr;
-    if (ptrCopy != nullptr) {
-      ptr = nullptr;
-      disposer->dispose(const_cast<RemoveConst<T>*>(ptrCopy));
-    }
-  }
-
-  template <typename U>
-  friend class Own;
-  friend class Maybe<Own<T>>;
-};
-
-namespace _ {  // private
-
-template <typename T>
-class OwnOwn {
-public:
-  inline OwnOwn(Own<T>&& value) noexcept: value(kj::mv(value)) {}
-
-  inline Own<T>& operator*() & { return value; }
-  inline const Own<T>& operator*() const & { return value; }
-  inline Own<T>&& operator*() && { return kj::mv(value); }
-  inline const Own<T>&& operator*() const && { return kj::mv(value); }
-  inline Own<T>* operator->() { return &value; }
-  inline const Own<T>* operator->() const { return &value; }
-  inline operator Own<T>*() { return value ? &value : nullptr; }
-  inline operator const Own<T>*() const { return value ? &value : nullptr; }
-
-private:
-  Own<T> value;
-};
-
-template <typename T>
-OwnOwn<T> readMaybe(Maybe<Own<T>>&& maybe) { return OwnOwn<T>(kj::mv(maybe.ptr)); }
-template <typename T>
-Own<T>* readMaybe(Maybe<Own<T>>& maybe) { return maybe.ptr ? &maybe.ptr : nullptr; }
-template <typename T>
-const Own<T>* readMaybe(const Maybe<Own<T>>& maybe) { return maybe.ptr ? &maybe.ptr : nullptr; }
-
-}  // namespace _ (private)
-
-template <typename T>
-class Maybe<Own<T>> {
-public:
-  inline Maybe(): ptr(nullptr) {}
-  inline Maybe(Own<T>&& t) noexcept: ptr(kj::mv(t)) {}
-  inline Maybe(Maybe&& other) noexcept: ptr(kj::mv(other.ptr)) {}
-
-  template <typename U>
-  inline Maybe(Maybe<Own<U>>&& other): ptr(mv(other.ptr)) {}
-
-  inline Maybe(decltype(nullptr)) noexcept: ptr(nullptr) {}
-
-  inline operator Maybe<T&>() { return ptr.get(); }
-  inline operator Maybe<const T&>() const { return ptr.get(); }
-
-  inline Maybe& operator=(Maybe&& other) { ptr = kj::mv(other.ptr); return *this; }
-
-  inline bool operator==(decltype(nullptr)) const { return ptr == nullptr; }
-  inline bool operator!=(decltype(nullptr)) const { return ptr != nullptr; }
-
-  Own<T>& orDefault(Own<T>& defaultValue) {
-    if (ptr == nullptr) {
-      return defaultValue;
-    } else {
-      return ptr;
-    }
-  }
-  const Own<T>& orDefault(const Own<T>& defaultValue) const {
-    if (ptr == nullptr) {
-      return defaultValue;
-    } else {
-      return ptr;
-    }
-  }
-
-  template <typename Func>
-  auto map(Func&& f) & -> Maybe<decltype(f(instance<Own<T>&>()))> {
-    if (ptr == nullptr) {
-      return nullptr;
-    } else {
-      return f(ptr);
-    }
-  }
-
-  template <typename Func>
-  auto map(Func&& f) const & -> Maybe<decltype(f(instance<const Own<T>&>()))> {
-    if (ptr == nullptr) {
-      return nullptr;
-    } else {
-      return f(ptr);
-    }
-  }
-
-  template <typename Func>
-  auto map(Func&& f) && -> Maybe<decltype(f(instance<Own<T>&&>()))> {
-    if (ptr == nullptr) {
-      return nullptr;
-    } else {
-      return f(kj::mv(ptr));
-    }
-  }
-
-  template <typename Func>
-  auto map(Func&& f) const && -> Maybe<decltype(f(instance<const Own<T>&&>()))> {
-    if (ptr == nullptr) {
-      return nullptr;
-    } else {
-      return f(kj::mv(ptr));
-    }
-  }
-
-private:
-  Own<T> ptr;
-
-  template <typename U>
-  friend class Maybe;
-  template <typename U>
-  friend _::OwnOwn<U> _::readMaybe(Maybe<Own<U>>&& maybe);
-  template <typename U>
-  friend Own<U>* _::readMaybe(Maybe<Own<U>>& maybe);
-  template <typename U>
-  friend const Own<U>* _::readMaybe(const Maybe<Own<U>>& maybe);
-};
-
-namespace _ {  // private
-
-template <typename T>
-class HeapDisposer final: public Disposer {
-public:
-  virtual void disposeImpl(void* pointer) const override { delete reinterpret_cast<T*>(pointer); }
-
-  static const HeapDisposer instance;
-};
-
-template <typename T>
-const HeapDisposer<T> HeapDisposer<T>::instance = HeapDisposer<T>();
-
-}  // namespace _ (private)
-
-template <typename T, typename... Params>
-Own<T> heap(Params&&... params) {
-  // heap<T>(...) allocates a T on the heap, forwarding the parameters to its constructor.  The
-  // exact heap implementation is unspecified -- for now it is operator new, but you should not
-  // assume this.  (Since we know the object size at delete time, we could actually implement an
-  // allocator that is more efficient than operator new.)
-
-  return Own<T>(new T(kj::fwd<Params>(params)...), _::HeapDisposer<T>::instance);
-}
-
-template <typename T>
-Own<Decay<T>> heap(T&& orig) {
-  // Allocate a copy (or move) of the argument on the heap.
-  //
-  // The purpose of this overload is to allow you to omit the template parameter as there is only
-  // one argument and the purpose is to copy it.
-
-  typedef Decay<T> T2;
-  return Own<T2>(new T2(kj::fwd<T>(orig)), _::HeapDisposer<T2>::instance);
-}
-
-// =======================================================================================
-// SpaceFor<T> -- assists in manual allocation
-
-template <typename T>
-class SpaceFor {
-  // A class which has the same size and alignment as T but does not call its constructor or
-  // destructor automatically.  Instead, call construct() to construct a T in the space, which
-  // returns an Own<T> which will take care of calling T's destructor later.
-
-public:
-  inline SpaceFor() {}
-  inline ~SpaceFor() {}
-
-  template <typename... Params>
-  Own<T> construct(Params&&... params) {
-    ctor(value, kj::fwd<Params>(params)...);
-    return Own<T>(&value, DestructorOnlyDisposer<T>::instance);
-  }
-
-private:
-  union {
-    T value;
-  };
-};
-
-// =======================================================================================
-// Inline implementation details
-
-template <typename T>
-struct Disposer::Dispose_<T, true> {
-  static void dispose(T* object, const Disposer& disposer) {
-    // Note that dynamic_cast<void*> does not require RTTI to be enabled, because the offset to
-    // the top of the object is in the vtable -- as it obviously needs to be to correctly implement
-    // operator delete.
-    disposer.disposeImpl(dynamic_cast<void*>(object));
-  }
-};
-template <typename T>
-struct Disposer::Dispose_<T, false> {
-  static void dispose(T* object, const Disposer& disposer) {
-    disposer.disposeImpl(static_cast<void*>(object));
-  }
-};
-
-template <typename T>
-void Disposer::dispose(T* object) const {
-  Dispose_<T>::dispose(object, *this);
-}
-
-}  // namespace kj
-
-#endif  // KJ_MEMORY_H_
+// Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
+// Licensed under the MIT License:
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+#ifndef KJ_MEMORY_H_
+#define KJ_MEMORY_H_
+
+#if defined(__GNUC__) && !KJ_HEADER_WARNINGS
+#pragma GCC system_header
+#endif
+
+#include "common.h"
+
+namespace kj {
+
+// =======================================================================================
+// Disposer -- Implementation details.
+
+class Disposer {
+  // Abstract interface for a thing that "disposes" of objects, where "disposing" usually means
+  // calling the destructor followed by freeing the underlying memory.  `Own<T>` encapsulates an
+  // object pointer with corresponding Disposer.
+  //
+  // Few developers will ever touch this interface.  It is primarily useful for those implementing
+  // custom memory allocators.
+
+protected:
+  // Do not declare a destructor, as doing so will force a global initializer for each HeapDisposer
+  // instance.  Eww!
+
+  virtual void disposeImpl(void* pointer) const = 0;
+  // Disposes of the object, given a pointer to the beginning of the object.  If the object is
+  // polymorphic, this pointer is determined by dynamic_cast<void*>().  For non-polymorphic types,
+  // Own<T> does not allow any casting, so the pointer exactly matches the original one given to
+  // Own<T>.
+
+public:
+
+  template <typename T>
+  void dispose(T* object) const;
+  // Helper wrapper around disposeImpl().
+  //
+  // If T is polymorphic, calls `disposeImpl(dynamic_cast<void*>(object))`, otherwise calls
+  // `disposeImpl(implicitCast<void*>(object))`.
+  //
+  // Callers must not call dispose() on the same pointer twice, even if the first call throws
+  // an exception.
+
+private:
+  template <typename T, bool polymorphic = __is_polymorphic(T)>
+  struct Dispose_;
+};
+
+template <typename T>
+class DestructorOnlyDisposer: public Disposer {
+  // A disposer that merely calls the type's destructor and nothing else.
+
+public:
+  static const DestructorOnlyDisposer instance;
+
+  void disposeImpl(void* pointer) const override {
+    reinterpret_cast<T*>(pointer)->~T();
+  }
+};
+
+template <typename T>
+const DestructorOnlyDisposer<T> DestructorOnlyDisposer<T>::instance = DestructorOnlyDisposer<T>();
+
+class NullDisposer: public Disposer {
+  // A disposer that does nothing.
+
+public:
+  static const NullDisposer instance;
+
+  void disposeImpl(void* pointer) const override {}
+};
+
+// =======================================================================================
+// Own<T> -- An owned pointer.
+
+template <typename T>
+class Own {
+  // A transferrable title to a T.  When an Own<T> goes out of scope, the object's Disposer is
+  // called to dispose of it.  An Own<T> can be efficiently passed by move, without relocating the
+  // underlying object; this transfers ownership.
+  //
+  // This is much like std::unique_ptr, except:
+  // - You cannot release().  An owned object is not necessarily allocated with new (see next
+  //   point), so it would be hard to use release() correctly.
+  // - The deleter is made polymorphic by virtual call rather than by template.  This is much
+  //   more powerful -- it allows the use of custom allocators, freelists, etc.  This could
+  //   _almost_ be accomplished with unique_ptr by forcing everyone to use something like
+  //   std::unique_ptr<T, kj::Deleter>, except that things get hairy in the presence of multiple
+  //   inheritance and upcasting, and anyway if you force everyone to use a custom deleter
+  //   then you've lost any benefit to interoperating with the "standard" unique_ptr.
+
+public:
+  KJ_DISALLOW_COPY(Own);
+  inline Own(): disposer(nullptr), ptr(nullptr) {}
+  inline Own(Own&& other) noexcept
+      : disposer(other.disposer), ptr(other.ptr) { other.ptr = nullptr; }
+  inline Own(Own<RemoveConstOrDisable<T>>&& other) noexcept
+      : disposer(other.disposer), ptr(other.ptr) { other.ptr = nullptr; }
+  template <typename U, typename = EnableIf<canConvert<U*, T*>()>>
+  inline Own(Own<U>&& other) noexcept
+      : disposer(other.disposer), ptr(other.ptr) {
+    static_assert(__is_polymorphic(T),
+        "Casting owned pointers requires that the target type is polymorphic.");
+    other.ptr = nullptr;
+  }
+  inline Own(T* ptr, const Disposer& disposer) noexcept: disposer(&disposer), ptr(ptr) {}
+
+  ~Own() noexcept(false) { dispose(); }
+
+  inline Own& operator=(Own&& other) {
+    // Move-assingnment operator.
+
+    // Careful, this might own `other`.  Therefore we have to transfer the pointers first, then
+    // dispose.
+    const Disposer* disposerCopy = disposer;
+    T* ptrCopy = ptr;
+    disposer = other.disposer;
+    ptr = other.ptr;
+    other.ptr = nullptr;
+    if (ptrCopy != nullptr) {
+      disposerCopy->dispose(const_cast<RemoveConst<T>*>(ptrCopy));
+    }
+    return *this;
+  }
+
+  inline Own& operator=(decltype(nullptr)) {
+    dispose();
+    return *this;
+  }
+
+  template <typename U>
+  Own<U> downcast() {
+    // Downcast the pointer to Own<U>, destroying the original pointer.  If this pointer does not
+    // actually point at an instance of U, the results are undefined (throws an exception in debug
+    // mode if RTTI is enabled, otherwise you're on your own).
+
+    Own<U> result;
+    if (ptr != nullptr) {
+      result.ptr = &kj::downcast<U>(*ptr);
+      result.disposer = disposer;
+      ptr = nullptr;
+    }
+    return result;
+  }
+
+#define NULLCHECK KJ_IREQUIRE(ptr != nullptr, "null Own<> dereference")
+  inline T* operator->() { NULLCHECK; return ptr; }
+  inline const T* operator->() const { NULLCHECK; return ptr; }
+  inline T& operator*() { NULLCHECK; return *ptr; }
+  inline const T& operator*() const { NULLCHECK; return *ptr; }
+#undef NULLCHECK
+  inline T* get() { return ptr; }
+  inline const T* get() const { return ptr; }
+  inline operator T*() { return ptr; }
+  inline operator const T*() const { return ptr; }
+
+private:
+  const Disposer* disposer;  // Only valid if ptr != nullptr.
+  T* ptr;
+
+  inline explicit Own(decltype(nullptr)): disposer(nullptr), ptr(nullptr) {}
+
+  inline bool operator==(decltype(nullptr)) { return ptr == nullptr; }
+  inline bool operator!=(decltype(nullptr)) { return ptr != nullptr; }
+  // Only called by Maybe<Own<T>>.
+
+  inline void dispose() {
+    // Make sure that if an exception is thrown, we are left with a null ptr, so we won't possibly
+    // dispose again.
+    T* ptrCopy = ptr;
+    if (ptrCopy != nullptr) {
+      ptr = nullptr;
+      disposer->dispose(const_cast<RemoveConst<T>*>(ptrCopy));
+    }
+  }
+
+  template <typename U>
+  friend class Own;
+  friend class Maybe<Own<T>>;
+};
+
+namespace _ {  // private
+
+template <typename T>
+class OwnOwn {
+public:
+  inline OwnOwn(Own<T>&& value) noexcept: value(kj::mv(value)) {}
+
+  inline Own<T>& operator*() & { return value; }
+  inline const Own<T>& operator*() const & { return value; }
+  inline Own<T>&& operator*() && { return kj::mv(value); }
+  inline const Own<T>&& operator*() const && { return kj::mv(value); }
+  inline Own<T>* operator->() { return &value; }
+  inline const Own<T>* operator->() const { return &value; }
+  inline operator Own<T>*() { return value ? &value : nullptr; }
+  inline operator const Own<T>*() const { return value ? &value : nullptr; }
+
+private:
+  Own<T> value;
+};
+
+template <typename T>
+OwnOwn<T> readMaybe(Maybe<Own<T>>&& maybe) { return OwnOwn<T>(kj::mv(maybe.ptr)); }
+template <typename T>
+Own<T>* readMaybe(Maybe<Own<T>>& maybe) { return maybe.ptr ? &maybe.ptr : nullptr; }
+template <typename T>
+const Own<T>* readMaybe(const Maybe<Own<T>>& maybe) { return maybe.ptr ? &maybe.ptr : nullptr; }
+
+}  // namespace _ (private)
+
+template <typename T>
+class Maybe<Own<T>> {
+public:
+  inline Maybe(): ptr(nullptr) {}
+  inline Maybe(Own<T>&& t) noexcept: ptr(kj::mv(t)) {}
+  inline Maybe(Maybe&& other) noexcept: ptr(kj::mv(other.ptr)) {}
+
+  template <typename U>
+  inline Maybe(Maybe<Own<U>>&& other): ptr(mv(other.ptr)) {}
+  template <typename U>
+  inline Maybe(Own<U>&& other): ptr(mv(other)) {}
+
+  inline Maybe(decltype(nullptr)) noexcept: ptr(nullptr) {}
+
+  inline operator Maybe<T&>() { return ptr.get(); }
+  inline operator Maybe<const T&>() const { return ptr.get(); }
+
+  inline Maybe& operator=(Maybe&& other) { ptr = kj::mv(other.ptr); return *this; }
+
+  inline bool operator==(decltype(nullptr)) const { return ptr == nullptr; }
+  inline bool operator!=(decltype(nullptr)) const { return ptr != nullptr; }
+
+  Own<T>& orDefault(Own<T>& defaultValue) {
+    if (ptr == nullptr) {
+      return defaultValue;
+    } else {
+      return ptr;
+    }
+  }
+  const Own<T>& orDefault(const Own<T>& defaultValue) const {
+    if (ptr == nullptr) {
+      return defaultValue;
+    } else {
+      return ptr;
+    }
+  }
+
+  template <typename Func>
+  auto map(Func&& f) & -> Maybe<decltype(f(instance<Own<T>&>()))> {
+    if (ptr == nullptr) {
+      return nullptr;
+    } else {
+      return f(ptr);
+    }
+  }
+
+  template <typename Func>
+  auto map(Func&& f) const & -> Maybe<decltype(f(instance<const Own<T>&>()))> {
+    if (ptr == nullptr) {
+      return nullptr;
+    } else {
+      return f(ptr);
+    }
+  }
+
+  template <typename Func>
+  auto map(Func&& f) && -> Maybe<decltype(f(instance<Own<T>&&>()))> {
+    if (ptr == nullptr) {
+      return nullptr;
+    } else {
+      return f(kj::mv(ptr));
+    }
+  }
+
+  template <typename Func>
+  auto map(Func&& f) const && -> Maybe<decltype(f(instance<const Own<T>&&>()))> {
+    if (ptr == nullptr) {
+      return nullptr;
+    } else {
+      return f(kj::mv(ptr));
+    }
+  }
+
+private:
+  Own<T> ptr;
+
+  template <typename U>
+  friend class Maybe;
+  template <typename U>
+  friend _::OwnOwn<U> _::readMaybe(Maybe<Own<U>>&& maybe);
+  template <typename U>
+  friend Own<U>* _::readMaybe(Maybe<Own<U>>& maybe);
+  template <typename U>
+  friend const Own<U>* _::readMaybe(const Maybe<Own<U>>& maybe);
+};
+
+namespace _ {  // private
+
+template <typename T>
+class HeapDisposer final: public Disposer {
+public:
+  virtual void disposeImpl(void* pointer) const override { delete reinterpret_cast<T*>(pointer); }
+
+  static const HeapDisposer instance;
+};
+
+template <typename T>
+const HeapDisposer<T> HeapDisposer<T>::instance = HeapDisposer<T>();
+
+}  // namespace _ (private)
+
+template <typename T, typename... Params>
+Own<T> heap(Params&&... params) {
+  // heap<T>(...) allocates a T on the heap, forwarding the parameters to its constructor.  The
+  // exact heap implementation is unspecified -- for now it is operator new, but you should not
+  // assume this.  (Since we know the object size at delete time, we could actually implement an
+  // allocator that is more efficient than operator new.)
+
+  return Own<T>(new T(kj::fwd<Params>(params)...), _::HeapDisposer<T>::instance);
+}
+
+template <typename T>
+Own<Decay<T>> heap(T&& orig) {
+  // Allocate a copy (or move) of the argument on the heap.
+  //
+  // The purpose of this overload is to allow you to omit the template parameter as there is only
+  // one argument and the purpose is to copy it.
+
+  typedef Decay<T> T2;
+  return Own<T2>(new T2(kj::fwd<T>(orig)), _::HeapDisposer<T2>::instance);
+}
+
+// =======================================================================================
+// SpaceFor<T> -- assists in manual allocation
+
+template <typename T>
+class SpaceFor {
+  // A class which has the same size and alignment as T but does not call its constructor or
+  // destructor automatically.  Instead, call construct() to construct a T in the space, which
+  // returns an Own<T> which will take care of calling T's destructor later.
+
+public:
+  inline SpaceFor() {}
+  inline ~SpaceFor() {}
+
+  template <typename... Params>
+  Own<T> construct(Params&&... params) {
+    ctor(value, kj::fwd<Params>(params)...);
+    return Own<T>(&value, DestructorOnlyDisposer<T>::instance);
+  }
+
+private:
+  union {
+    T value;
+  };
+};
+
+// =======================================================================================
+// Inline implementation details
+
+template <typename T>
+struct Disposer::Dispose_<T, true> {
+  static void dispose(T* object, const Disposer& disposer) {
+    // Note that dynamic_cast<void*> does not require RTTI to be enabled, because the offset to
+    // the top of the object is in the vtable -- as it obviously needs to be to correctly implement
+    // operator delete.
+    disposer.disposeImpl(dynamic_cast<void*>(object));
+  }
+};
+template <typename T>
+struct Disposer::Dispose_<T, false> {
+  static void dispose(T* object, const Disposer& disposer) {
+    disposer.disposeImpl(static_cast<void*>(object));
+  }
+};
+
+template <typename T>
+void Disposer::dispose(T* object) const {
+  Dispose_<T>::dispose(object, *this);
+}
+
+}  // namespace kj
+
+#endif  // KJ_MEMORY_H_