SERVER-26025 Smart pointer with clone on copy

This clonable pointer works like a unique_ptr, but upon
copy it invokes a customizable cloning function.  A `clone`
member function is used by default.  There exist several
customization points.

12 files changed, 2031 insertions, 0 deletions

diff --git a/src/mongo/base/SConscript b/src/mongo/base/SConscript
index 848aca3b7f0..af40fdab72a 100644
--- a/src/mongo/base/SConscript
+++ b/src/mongo/base/SConscript
@@ -55,6 +55,15 @@ env.CppUnitTest(
     ],
 )
 
+env.CppUnitTest(
+    target=[
+        'clonable_ptr_test',
+    ],
+    source=[
+        'clonable_ptr_test.cpp',
+    ],
+)
+
 env.Library(
     target=[
         'secure_allocator'
diff --git a/src/mongo/base/clonable_ptr.h b/src/mongo/base/clonable_ptr.h
new file mode 100644
index 00000000000..0b718db4d5d
--- /dev/null
+++ b/src/mongo/base/clonable_ptr.h
@@ -0,0 +1,648 @@
+// clonable_ptr.h
+
+/*-
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects
+ *    for all of the code used other than as permitted herein. If you modify
+ *    file(s) with this exception, you may extend this exception to your
+ *    version of the file(s), but you are not obligated to do so. If you do not
+ *    wish to do so, delete this exception statement from your version. If you
+ *    delete this exception statement from all source files in the program,
+ *    then also delete it in the license file.
+ */
+
+#pragma once
+
+#include <cstddef>
+#include <memory>
+#include <tuple>
+#include <type_traits>
+
+namespace mongo {
+namespace clonable_ptr_detail {
+// This is the default `CloneFactory` conforming to `mongo::concept::CloneFactory` for
+// `clonable_ptr`.
+template <typename Clonable>
+struct CloneFactory {
+    auto operator()(const Clonable& c) const -> decltype(c.clone()) {
+        return c.clone();
+    }
+};
+
+// TODO: Move some of these traits detection structs to a template metaprogramming header.
+template <typename T>
+struct detect_clone_factory_type_member_impl {
+    struct Fallback {
+        struct clone_factory_type {};
+    };
+
+    struct Derived : T, Fallback {};
+
+    using Yes = char[2];
+    using No = char[1];
+
+    template <typename U>
+    static No& test(typename U::clone_factory_type*);
+
+    template <typename U>
+    static Yes& test(U*);
+
+    static constexpr bool value = sizeof(test<Derived>(0)) == sizeof(Yes);
+
+    using type = typename std::integral_constant<bool, value>::type;
+};
+
+template <typename T>
+struct detect_clone_factory_type_member : std::conditional<std::is_class<T>::value,
+                                                           detect_clone_factory_type_member_impl<T>,
+                                                           std::false_type>::type {};
+
+template <typename T, bool has_clone_factory_member = detect_clone_factory_type_member<T>::value>
+struct clonable_traits_impl;
+
+template <typename T>
+struct clonable_traits_impl<T, false> {
+    using clone_factory_type = CloneFactory<T>;
+};
+
+template <typename T>
+struct clonable_traits_impl<T, true> {
+    using clone_factory_type = typename T::clone_factory_type;
+};
+}  // namespace clonable_ptr_detail
+
+/**
+ * The 'clonable_traits' class is a specializable traits class for clonable-like types.  By
+ * specializing this traits class for a type it is possible to change the global default
+ * `CloneFactory` type for a specific type.  Types which conform to `mongo::concept::Clonable`
+ * will get a default `CloneFactory` type whch invokes their specific `Clonable::clone` function.  A
+ * specialization can be used to make a type use a different clone factory function.  A type `T` may
+ * specify `T::clone_factory_type` instead of specializing this traits type.
+ */
+template <typename T>
+struct clonable_traits : clonable_ptr_detail::clonable_traits_impl<T> {};
+
+/**
+ * The `clonable_ptr` represents a value-like type held at a distance.  The `clonable_ptr` class is
+ * a smart-pointer type which functions like a `std::unique_ptr` with the added ability to create
+ * new copies of the pointee on copy construction.  The default CloneFactory assumes that `T` is a
+ * type which models the Concept `mongo::concept::Clonable`.  The supplied type may supply an
+ * alternative default `CloneFactory` type by either of two means:
+ *
+ *  * `T` may define a member `T::clone_factory_type` which conforms to
+ *    `mongo::concept::CloneFactory`
+ *  * `T` may have an accompanying specialization of `mongo::clonable_traits< T >` which
+ *    defines `clonable_factory_type`.
+ *
+ * NOTE: The `CloneFactory` type is permitted to be stateful, but must be copy constructible and
+ * copy assignable.
+ * NOTE: The `CloneFactory` member does NOT participate in value comparisons for a `clonable_ptr`,
+ * even when it has state.
+ *
+ * `T`: The type of the object being managed.
+ * `CloneFactory`: A type which models the Concept `mongo::concept::CloneFactory`.
+ * `UniquePtr`: A type which models the Concept `mongo::concept::UniquePtr`
+ */
+template <typename T,
+          typename CloneFactory = typename clonable_traits<T>::clone_factory_type,
+          template <typename, typename...> class UniquePtr = std::unique_ptr>
+class clonable_ptr {
+private:
+    // `std::tuple` is used to avoid allocating storage for `cloneFactory` if it is a non-storage
+    // type.
+    std::tuple<CloneFactory, UniquePtr<T>> data;
+
+    inline const CloneFactory& cloneFactory() const {
+        return std::get<0>(data);
+    }
+
+    inline const UniquePtr<T>& ptr() const {
+        return std::get<1>(data);
+    }
+
+    inline UniquePtr<T>& ptr() {
+        return std::get<1>(data);
+    }
+
+    inline const auto& _makeEqualityLens() const noexcept {
+        return this->ptr();
+    }
+
+    inline const auto& _makeStrictWeakOrderLens() const noexcept {
+        return this->ptr();
+    }
+
+    static inline UniquePtr<T> clone_with_factory_impl(const T& copy, const CloneFactory& factory) {
+        return UniquePtr<T>{factory(copy)};
+    }
+
+    template <typename Pointerlike>
+    static inline UniquePtr<T> clone_with_factory(Pointerlike&& copy, const CloneFactory& factory) {
+        if (!copy)
+            return nullptr;
+        return clone_with_factory_impl(*copy, factory);
+    }
+
+    struct internal_construction {};
+
+    explicit inline clonable_ptr(UniquePtr<T>&& p,
+                                 const CloneFactory* const f,
+                                 const internal_construction&)
+        : data(*f, std::move(p)) {}
+
+    explicit inline clonable_ptr(UniquePtr<T>&& p, CloneFactory&& f, const internal_construction&)
+        : data(std::move(f), std::move(p)) {}
+
+public:
+    /*! Destroys this pointer.  Functions like `std::unique_ptr`. */
+    inline ~clonable_ptr() noexcept = default;
+
+    /*! Moves a value, by pointer.  Functions like `std::unique_ptr`. */
+    inline clonable_ptr(clonable_ptr&&) noexcept(
+        noexcept(CloneFactory{std::declval<CloneFactory>()}) &&
+        noexcept(UniquePtr<T>{std::declval<UniquePtr<T>>()})) = default;
+
+    /*! Moves a value, by pointer.  Functions like `std::unique_ptr`. */
+    inline clonable_ptr& operator=(clonable_ptr&&) &
+        noexcept(noexcept(std::declval<CloneFactory>() = std::declval<CloneFactory>()) &&
+                 noexcept(std::declval<UniquePtr<T>>() = std::declval<UniquePtr<T>>())) = default;
+
+    /*!
+     * Constructs a pointer referring to a new copy of an original value.  The old object owned by
+     * `*this` will be deleted, and `*this` will manage a new copy of `copy`, as created by
+     * `copy->clone()`.  If `copy` is not managing anything (its internal pointer is `nullptr`),
+     * then this new copy will also be nullptr.
+     *
+     * POST: `copy != nullptr ? copy != *this : copy == *this` -- If `copy` stores a pointer to a
+     * value, then `*this` will have an independent pointer.  If `copy` stores `nullptr`, then
+     * `*this` will also store `nullptr`.
+     *
+     * `copy`: The original value to copy.
+     * THROWS: Any exceptions thrown by `cloneFactory( *copy )`.
+     * TODO: Consider adding a noexcept deduction specifier to this copy operation.
+     */
+    inline clonable_ptr(const clonable_ptr& copy)
+        : data{copy.cloneFactory(), clone_with_factory(copy, copy.cloneFactory())} {}
+
+    /*!
+     * Constructs a pointer referring to a new copy of an original value.  The old object owned by
+     * `*this` will be deleted, and `*this` will manage a new copy of `copy`, as created by
+     * `copy->clone()`.  If `copy` is not managing anything (its internal pointer is `nullptr`),
+     * then this new copy will also be nullptr.
+     *
+     * POST: `copy != nullptr ? copy != *this : copy == *this` -- If `copy` stores a pointer to a
+     * value, then `*this` will have an independent pointer.  If `copy` stores `nullptr`, then
+     * `*this` will also store `nullptr`.
+     *
+     * NOTE: The `CloneFactory` will be copied from the `copy` poiner, by default.
+     *
+     * `copy`: The original value to copy.
+     * `factory`: The factory to use for cloning.  Defaults to the source's factory.
+     * THROWS: Any exceptions thrown by `factory( *copy )`.
+     * TODO: Consider adding a noexcept deduction specifier to this copy operation.
+     */
+    inline clonable_ptr(const clonable_ptr& copy, const CloneFactory& factory)
+        : data{factory, clone_with_factory(copy, factory)} {}
+
+    /*!
+     * Changes the value of this pointer, by creating a new object having the same value as `copy`.
+     * The old object owned by `*this` will be deleted, and `*this` will manage a new copy of
+     * `copy`, as created by `copy->clone()`.  If `copy` is not managing anything (its internal
+     * pointer is `nullptr`), then this new copy will also be nullptr.
+     *
+     * NOTE: This operation cannot be conducted on an xvalue or prvalue instance.  (This prevents
+     * silliness such as: `func_returning_ptr()= some_other_func_returning_ptr();`)
+     *
+     * NOTE: `copy`'s `CloneFactory` will be used to copy.
+     *
+     * POST: `copy != nullptr ? copy != *this : copy == *this` -- If `copy` stores a pointer to a
+     * value, then `*this` will have an independent pointer.  If `copy` stores `nullptr`, then
+     * `*this` will also store `nullptr`.
+     *
+     * `copy`: The value to make a copy of.
+     * RETURNS: A reference to this pointer, after modification.
+     * TODO: Consider adding a noexcept deduction specifier to this copy operation.
+     */
+    inline clonable_ptr& operator=(const clonable_ptr& copy) & {
+        return *this = clonable_ptr{copy};
+    }
+
+    // Maintenance note: The two enable_if overloads of `clonable_ptr( std::nullptr_t )` are
+    // necessary, due to the fact that `std::nullptr_t` is capable of implicit conversion to a
+    // built-in pointer type.  If the stateful form being deleted causes the `nullptr` to convert,
+    // this could cause binding to another ctor which may be undesired.
+
+    /*!
+     * `nullptr` construct a clonable pointer (to `nullptr`), if the `CloneFactory` type is
+     * stateless.
+     * The value will be a pointer to nothing, with a default `CloneFactory`.
+     * NOTE: This constructor is only available for types with a stateless `CloneFactory` type.
+     */
+    template <typename CloneFactory_ = CloneFactory>
+    inline clonable_ptr(
+        typename std::enable_if<std::is_empty<CloneFactory_>::value, std::nullptr_t>::type) {}
+
+    /*!
+     * Disable `nullptr` construction of clonable pointer (to `nullptr`), if the `CloneFactory` type
+     * is stateful.
+     * NOTE: This constructor is disabled for types with a stateless `CloneFactory` type.
+     */
+    template <typename CloneFactory_ = CloneFactory>
+    inline clonable_ptr(typename std::enable_if<!std::is_empty<CloneFactory_>::value,
+                                                std::nullptr_t>::type) = delete;
+
+    /*!
+     * Constructs a pointer to nothing, with a default `CloneFactory`.
+     * This function is unavailable when `CloneFactory` is stateful.
+     */
+    template <typename CloneFactory_ = CloneFactory,
+              typename = typename std::enable_if<std::is_empty<CloneFactory_>::value>::type>
+    explicit inline clonable_ptr() noexcept {}
+
+    /*! Constructs a pointer to nothing, with the specified `CloneFactory`. */
+    explicit inline clonable_ptr(CloneFactory factory) : data{factory, nullptr} {}
+
+    /*!
+     * Constructs a `clonable_ptr` which owns `p`, initializing the stored pointer with `p`.
+     * This function is unavailable when `CloneFactory` is stateful.
+     * `p`: The pointer to take ownership of.
+     */
+    template <typename CloneFactory_ = CloneFactory>
+    explicit inline clonable_ptr(
+        typename std::enable_if<std::is_empty<CloneFactory_>::value, T* const>::type p)
+        : clonable_ptr(UniquePtr<T>{p}) {}
+
+    /*!
+     * Disable single-argument construction of clonable pointer (with a raw pointer), if the
+     * `CloneFactory` type is stateful.
+     * NOTE: This constructor is disabled for types with a stateless `CloneFactory` type.
+     */
+    template <typename CloneFactory_ = CloneFactory>
+    explicit inline clonable_ptr(
+        typename std::enable_if<!std::is_empty<CloneFactory_>::value, T* const>::type) = delete;
+
+    // The reason that we have two overloads for clone factory is to ensure that we avoid as many
+    // exception-unsafe uses as possible.  The const-lvalue-reference variant in conjunction with
+    // the rvalue-reference variant lets us separate the cases of "constructed in place" from
+    // "passed from a local".  In the latter case, we can't make our type any safer, since the
+    // timing of the construction of the local and the timing of the `new` on the raw pointer are
+    // out of our control.  At least we prevent an accidental use which SEEMS exception safe but
+    // isn't -- hopefully highlighting exception unsafe code, by making it more explicit.  In the
+    // former, "constructed in place", case, we are able to successfully move construct without
+    // exception problems, if it's nothrow move constructible.  If it isn't we flag a compiler
+    // error.  In this case, too, we prevent accidental use which SEEMS exception safe and hopefully
+    // will similarly highlight exception unsafe code.
+
+    /*!
+     * Constructs a `clonable_ptr` which owns `p`, initializing the stored pointer with `p`.  The
+     * `factory` parameter will be used as the `CloneFactory`
+     * `p`: The pointer to take ownership of.
+     * `factory`: The clone factory to use in future copies.
+     * NOTE: It is not recommended to use this constructor, as the following is not exception safe
+     * code:
+     * ~~~
+     * std::function<T* ()> cloner= [](const T& p){ return p; };
+     * auto getCloner= [=]{ return cloner; };
+     * clonable_ptr<T, std::function<T* ()>> bad{new T, getCloner()}; // BAD IDEA!!!
+     * ~~~
+     * Even if the above could be made exception safe, there are other more complicated use cases
+     * which would not be exception safe.  (The above is not exception safe, because the `new T`
+     * expression can be evaluated before the `getCloner()` expression is evaluated.  `getCloner()`
+     * is allowed to throw, thus leaving `new T` to be abandoned.
+     */
+    explicit inline clonable_ptr(T* const p, const CloneFactory& factory)
+        : clonable_ptr{UniquePtr<T>{p}, std::addressof(factory), internal_construction{}} {}
+
+    /*!
+     * We forbid construction of a `clonable_ptr` from an unmanaged pointer, when specifying
+     * a cloning function -- regardless of whether the `CloneFactory` is stateful or not.
+     * NOTE: We have disabled this constructor, as the following is not exception safe
+     * code:
+     * ~~~
+     * clonable_ptr<T, std::function<T* ()>> bad{new T, [](const T& p){ return p; }}; // BAD IDEA!!!
+     * ~~~
+     * Even if the above could be made exception safe, there are other more complicated use cases
+     * which would not be exception safe.  (The above is not exception safe, because the `new T`
+     * expression can be evaluated before the lambda expression is evaluated and converted to a
+     * `std::function`.  The `std::function` constructor is allowed to throw, thus leaving `new T`
+     * to be abandoned.  More complicated cases are completely hidden from `clonable_ptr`'s
+     * inspection, thus making this constructor too dangerous to exist.
+     */
+    explicit inline clonable_ptr(T* const p, CloneFactory&& factory) = delete;
+
+    /*!
+     * Constructs a `nullptr` valued clonable pointer, with a specified `CloneFactory`, `factory`.
+     */
+    explicit inline clonable_ptr(std::nullptr_t, CloneFactory&& factory)
+        : clonable_ptr{UniquePtr<T>{nullptr}, std::move(factory), internal_construction{}} {}
+
+    /*!
+     * Constructs a `clonable_ptr` by transferring ownership from `p` to `*this`.  A default
+     * `CloneFactory` will be provided for future copies.
+     * `p`: The pointer to take ownership of.
+     * NOTE: This constructor allows for implicit conversion from a `UniquePtr` (xvalue) object.
+     * NOTE: This constructor is unavailable when `CloneFactory` is stateful.
+     * NOTE: This usage should be preferred over the raw-pointer construction forms, when using
+     * factories as constructor arguments, as in the following exception safe code:
+     * ~~~
+     * clonable_ptr<T, std::function<T* ()>> good{std::make_unique<T>(),
+     *                                            [](const T& p){ return p; }}; // GOOD IDEA!!!
+     * ~~~
+     */
+    template <typename CloneFactory_ = CloneFactory,
+              typename Derived,
+              typename = typename std::enable_if<std::is_empty<CloneFactory_>::value>::type>
+    inline clonable_ptr(UniquePtr<Derived> p) : data{CloneFactory{}, std::move(p)} {}
+
+    /*!
+     * Constructs a `clonable_ptr` by transferring ownership from `p` to `*this`.  The `factory`
+     * parameter will be used as the `CloneFactory` for future copies.
+     * NOTE: This constructor allows for implicit conversion from a `UniquePtr` (xvalue) object.
+     * `p`: The pointer to take ownership of.
+     * `factory`: The clone factory to use in future copies.
+     * NOTE: This usage should be preferred over the raw-pointer construction forms, when using
+     * factories as constructor arguments, as in the following exception safe code:
+     * ~~~
+     * clonable_ptr<T, std::function<T* ()>> good{std::make_unique<T>(),
+     *                                            [](const T& p){ return p; }}; // GOOD IDEA!!!
+     * ~~~
+     */
+    template <typename Derived>
+    inline clonable_ptr(UniquePtr<Derived> p, CloneFactory factory)
+        : data{std::move(factory), std::move(p)} {}
+
+    /*!
+     * Changes the value of this pointer, by creating a new object having the same value as `copy`.
+     * The old object owned by `*this` will be deleted, and `*this` will manage a new copy of
+     * `copy`, as created by `copy->clone()`.  If `copy` is not managing anything (its internal
+     * pointer is `nullptr`), then this new copy will also be nullptr.
+     *
+     * NOTE: This operation cannot be performed on an xvalue or prvalue instance.  (This prevents
+     * silliness such as: `func_returning_ptr()= some_other_func_returning_ptr();`)
+     *
+     * NOTE: `copy`'s `CloneFactory` will be used to copy.
+     *
+     * POST: `copy != nullptr ? copy != *this : copy == *this` -- If `copy` stores a pointer to a
+     * value, then `*this` will have an independent pointer.  If `copy` stores `nullptr`, then
+     * `*this` will also store `nullptr`.
+     *
+     * `copy`: The value to make a copy of.
+     * RETURNS: A reference to this pointer, after modification.
+     */
+    inline clonable_ptr& operator=(UniquePtr<T> copy) & {
+        return *this = std::move(clonable_ptr{std::move(copy), this->cloneFactory()});
+    }
+
+    template <typename Derived>
+    inline clonable_ptr& operator=(UniquePtr<Derived> copy) & {
+        return *this = std::move(clonable_ptr{std::move(copy), this->cloneFactory()});
+    }
+
+    /*!
+     * Change the `CloneFactory` for `*this` to `factory`.
+     * NOTE: This operation cannot be performed on an xvalue or prvalue instance.  (This prevents
+     * silliness such as: `func_returning_ptr().setCloneFactory( factory );`.)
+     */
+    template <typename FactoryType>
+    inline void setCloneFactory(FactoryType&& factory) & {
+        this->cloneFactory() = std::forward<FactoryType>(factory);
+    }
+
+    /*!
+     * Dereferences the pointer owned by `*this`.
+     * NOTE: The behavior is undefined if `this->get() == nullptr`.
+     * RETURNS: The object owned by `*this`, equivalent to `*get()`.
+     */
+    inline auto& operator*() const {
+        return *this->ptr();
+    }
+
+    /*!
+     * Dereferences the pointer owned by `*this`.
+     * NOTE: The behavior is undefined if `this->get() == nullptr`.
+     * RETURNS: A pointer to the object owned by `*this`, equivalent to `get()`.
+     */
+    inline auto* operator-> () const {
+        return this->ptr().operator->();
+    }
+
+    /*!
+     * Returns `true` if `*this` owns a pointer to a value, and `false` otherwise.
+     * RETURNS: A value equivalent to `static_cast< bool >( this->get() )`.
+     */
+    explicit inline operator bool() const noexcept {
+        return this->ptr().get();
+    }
+
+    /*!
+     * Converts `*this` to a `UniquePtr< T >` by transferring ownership.  This function will retire
+     * ownership of the pointer owned by `*this`.  This is a safe operation, as this function cannot
+     * be called from an lvalue context -- rvalue operations are used to represent transfer of
+     * ownership semantics.
+     *
+     * NOTE: This function is only applicable in `rvalue` contexts.
+     * NOTE: This function has transfer of ownership semantics.
+     *
+     * RETURNS: A `UniquePtr< T >` which owns the pointer formerly managed by `*this`.
+     */
+    inline operator UniquePtr<T>() && {
+        return std::move(this->ptr());
+    }
+
+    /*! Provides a constant `UniquePtr< T >` view of the object owned by `*this`. */
+    inline operator const UniquePtr<T>&() const& {
+        return this->ptr();
+    }
+
+    /*! Provides a mutable `UniquePtr< T >` view of the object owned by `*this`. */
+    inline operator UniquePtr<T>&() & {
+        return this->ptr();
+    }
+
+    /*! Provides a C-style `T *` pointer to the object owned by `*this`. */
+    inline T* get() const {
+        return this->ptr().get();
+    }
+
+    inline void reset() & noexcept {
+        this->ptr().reset();
+    }
+
+    inline void reset(T* const p) & {
+        this->ptr().reset(p);
+    }
+
+    // Equality
+
+    inline friend bool operator==(const clonable_ptr& lhs, const clonable_ptr& rhs) {
+        return lhs._makeEqualityLens() == rhs._makeEqualityLens();
+    }
+
+    template <template <typename, typename...> class U, typename... UArgs>
+    inline friend bool operator==(const U<T, UArgs...>& lhs, const clonable_ptr& rhs) {
+        return lhs == rhs._makeEqualityLens();
+    }
+
+    template <template <typename, typename...> class U, typename... UArgs>
+    inline friend bool operator==(const clonable_ptr& lhs, const U<T, UArgs...>& rhs) {
+        return lhs._makeEqualityLens() == rhs;
+    }
+
+    inline friend bool operator==(const std::nullptr_t& lhs, const clonable_ptr& rhs) {
+        return lhs == rhs._makeEqualityLens();
+    }
+
+    inline friend bool operator==(const clonable_ptr& lhs, const std::nullptr_t& rhs) {
+        return lhs._makeEqualityLens() == rhs;
+    }
+
+    // Strict weak order
+
+    inline friend bool operator<(const clonable_ptr& lhs, const clonable_ptr& rhs) {
+        return lhs._makeStrictWeakOrderLens() < rhs._makeStrictWeakOrderLens();
+    }
+
+    template <template <typename, typename...> class U, typename... UArgs>
+    inline friend bool operator<(const U<T, UArgs...>& lhs, const clonable_ptr& rhs) {
+        return lhs < rhs._makeStrictWeakOrderLens();
+    }
+
+    template <template <typename, typename...> class U, typename... UArgs>
+    inline friend bool operator<(const clonable_ptr& lhs, const U<T, UArgs...>& rhs) {
+        return lhs._makeStrictWeakOrderLens() < rhs;
+    }
+
+    inline friend bool operator<(const std::nullptr_t& lhs, const clonable_ptr& rhs) {
+        return lhs < rhs._makeStrictWeakOrderLens();
+    }
+
+    inline friend bool operator<(const clonable_ptr& lhs, const std::nullptr_t& rhs) {
+        return lhs._makeStrictWeakOrderLens() < rhs;
+    }
+};
+
+// Inequality
+
+template <typename C, typename F, template <typename, typename...> class U>
+inline bool operator!=(const clonable_ptr<C, F, U>& lhs, const clonable_ptr<C, F, U>& rhs) {
+    return !(lhs == rhs);
+}
+
+template <typename C, typename F, template <typename, typename...> class U, typename... UArgs>
+inline bool operator!=(const U<C, UArgs...>& lhs, const clonable_ptr<C, F, U>& rhs) {
+    return !(lhs == rhs);
+}
+
+template <typename C, typename F, template <typename, typename...> class U, typename... UArgs>
+inline bool operator!=(const clonable_ptr<C, F, U>& lhs, const U<C, UArgs...>& rhs) {
+    return !(lhs == rhs);
+}
+
+template <typename C, typename F, template <typename, typename...> class U>
+inline bool operator!=(const std::nullptr_t& lhs, const clonable_ptr<C, F, U>& rhs) {
+    return !(lhs == rhs);
+}
+
+template <typename C, typename F, template <typename, typename...> class U>
+inline bool operator!=(const clonable_ptr<C, F, U>& lhs, const std::nullptr_t& rhs) {
+    return !(lhs == rhs);
+}
+
+// Greater than
+
+template <typename C, typename F, template <typename, typename...> class U>
+inline bool operator>(const clonable_ptr<C, F, U>& lhs, const clonable_ptr<C, F, U>& rhs) {
+    return rhs < lhs;
+}
+
+template <typename C, typename F, template <typename, typename...> class U, typename... UArgs>
+inline bool operator>(const U<C, UArgs...>& lhs, const clonable_ptr<C, F, U>& rhs) {
+    return rhs < lhs;
+}
+
+template <typename C, typename F, template <typename, typename...> class U, typename... UArgs>
+inline bool operator>(const clonable_ptr<C, F, U>& lhs, const U<C, UArgs...>& rhs) {
+    return rhs < lhs;
+}
+
+template <typename C, typename F, template <typename, typename...> class U>
+inline bool operator>(const std::nullptr_t& lhs, const clonable_ptr<C, F, U>& rhs) {
+    return rhs < lhs;
+}
+
+template <typename C, typename F, template <typename, typename...> class U>
+inline bool operator>(const clonable_ptr<C, F, U>& lhs, const std::nullptr_t& rhs) {
+    return rhs < lhs;
+}
+
+// Equal or Less
+
+template <typename C, typename F, template <typename, typename...> class U>
+inline bool operator<=(const clonable_ptr<C, F, U>& lhs, const clonable_ptr<C, F, U>& rhs) {
+    return !(lhs > rhs);
+}
+
+template <typename C, typename F, template <typename, typename...> class U, typename... UArgs>
+inline bool operator<=(const U<C, UArgs...>& lhs, const clonable_ptr<C, F, U>& rhs) {
+    return !(lhs > rhs);
+}
+
+template <typename C, typename F, template <typename, typename...> class U, typename... UArgs>
+inline bool operator<=(const clonable_ptr<C, F, U>& lhs, const U<C, UArgs...>& rhs) {
+    return !(lhs > rhs);
+}
+
+template <typename C, typename F, template <typename, typename...> class U>
+inline bool operator<=(const std::nullptr_t& lhs, const clonable_ptr<C, F, U>& rhs) {
+    return !(lhs > rhs);
+}
+
+template <typename C, typename F, template <typename, typename...> class U>
+inline bool operator<=(const clonable_ptr<C, F, U>& lhs, const std::nullptr_t& rhs) {
+    return !(lhs > rhs);
+}
+
+// Equal or greater
+
+template <typename C, typename F, template <typename, typename...> class U>
+inline bool operator>=(const clonable_ptr<C, F, U>& lhs, const clonable_ptr<C, F, U>& rhs) {
+    return !(lhs < rhs);
+}
+
+template <typename C, typename F, template <typename, typename...> class U, typename... UArgs>
+inline bool operator>=(const U<C, UArgs...>& lhs, const clonable_ptr<C, F, U>& rhs) {
+    return !(lhs < rhs);
+}
+
+template <typename C, typename F, template <typename, typename...> class U, typename... UArgs>
+inline bool operator>=(const clonable_ptr<C, F, U>& lhs, const U<C, UArgs...>& rhs) {
+    return !(lhs < rhs);
+}
+
+template <typename C, typename F, template <typename, typename...> class U>
+inline bool operator>=(const std::nullptr_t& lhs, const clonable_ptr<C, F, U>& rhs) {
+    return !(lhs < rhs);
+}
+
+template <typename C, typename F, template <typename, typename...> class U>
+inline bool operator>=(const clonable_ptr<C, F, U>& lhs, const std::nullptr_t& rhs) {
+    return !(lhs < rhs);
+}
+}  // namespace mongo
diff --git a/src/mongo/base/clonable_ptr_test.cpp b/src/mongo/base/clonable_ptr_test.cpp
new file mode 100644
index 00000000000..5554f1fbe6a
--- /dev/null
+++ b/src/mongo/base/clonable_ptr_test.cpp
@@ -0,0 +1,974 @@
+// clonable_ptr_test.cpp
+
+/*-
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects
+ *    for all of the code used other than as permitted herein. If you modify
+ *    file(s) with this exception, you may extend this exception to your
+ *    version of the file(s), but you are not obligated to do so. If you do not
+ *    wish to do so, delete this exception statement from your version. If you
+ *    delete this exception statement from all source files in the program,
+ *    then also delete it in the license file.
+ */
+
+#include "mongo/base/clonable_ptr.h"
+
+#include "mongo/stdx/functional.h"
+#include "mongo/stdx/memory.h"
+#include "mongo/unittest/unittest.h"
+
+#include <boost/lexical_cast.hpp>
+
+namespace {
+namespace stdx = mongo::stdx;
+
+// These testing helper classes model various kinds of class which should be compatible with
+// `mongo::clonable_ptr`.  The basic use cases satisfied by each class are described in each class's
+// documentation.
+
+// This class models the `Clonable` concept, and is used to test the simple case of `clonable_ptr`.
+class ClonableTest {
+private:
+    std::string data =
+        "This is the string data which is stored to make Functor Clonable need a complicated copy "
+        "ctor.";
+
+public:
+    std::unique_ptr<ClonableTest> clone() const {
+        return mongo::stdx::make_unique<ClonableTest>();
+    }
+};
+
+// This class provides a member structure which models `CloneFactory<AltClonableTest>`.  The member
+// structure is available under the expected member name of `clone_factory_type`.  The
+// `CloneFactory` is stateless.
+class AltClonableTest {
+private:
+    std::string data =
+        "This is the string data which is stored to make Functor Clonable need a complicated copy "
+        "ctor.";
+
+public:
+    struct clone_factory_type {
+        std::unique_ptr<AltClonableTest> operator()(const AltClonableTest&) const {
+            return mongo::stdx::make_unique<AltClonableTest>();
+        }
+    };
+};
+
+// This class requires a companion cloning function models `CloneFactory<Alt2ClonableTest>`.  There
+// is an attendant specialization of the `mongo::clonable_traits` metafunction to provide the clone
+// factory for this type.  That `CloneFactory` is stateless.
+class Alt2ClonableTest {
+private:
+    std::string data =
+        "This is the string data which is stored to make Functor Clonable need a complicated copy "
+        "ctor.";
+};
+}  // namespace
+
+namespace mongo {
+// This specialization of the `mongo::clonable_traits` metafunction provides a model of a stateless
+// `CloneFactory<Alt2ClonableTest>`
+template <>
+struct clonable_traits<::Alt2ClonableTest> {
+    struct clone_factory_type {
+        std::unique_ptr<Alt2ClonableTest> operator()(const Alt2ClonableTest&) const {
+            return mongo::stdx::make_unique<Alt2ClonableTest>();
+        }
+    };
+};
+}  // namespace mongo
+
+namespace {
+// This class uses a stateful cloning function provided by the `getCloningFunction` static member.
+// This stateful `CloneFactory<FunctorClonable>` must be passed to constructors of the
+// `cloning_ptr`.
+class FunctorClonable {
+private:
+    std::string data =
+        "This is the string data which is stored to make Functor Clonable need a complicated copy "
+        "ctor.";
+
+public:
+    using CloningFunctionType =
+        mongo::stdx::function<std::unique_ptr<FunctorClonable>(const FunctorClonable&)>;
+
+    static CloningFunctionType getCloningFunction() {
+        return
+            [](const FunctorClonable& c) { return mongo::stdx::make_unique<FunctorClonable>(c); };
+    }
+};
+
+
+// This class uses a stateful cloning function provided by the `getCloningFunction` static member.
+// This stateful `CloneFactory<FunctorWithDynamicStateClonable>` must be passed to constructors of
+// the `cloning_ptr`.  The `CloneFactory` for this type dynamically updates its internal state.
+// This is used to test cloning of objects that have dynamically changing clone factories.
+class FunctorWithDynamicStateClonable {
+private:
+    std::string data =
+        "This is the string data which is stored to make Functor Clonable need a complicated copy "
+        "ctor.";
+
+public:
+    FunctorWithDynamicStateClonable(const FunctorWithDynamicStateClonable&) = delete;
+    FunctorWithDynamicStateClonable() = default;
+
+    FunctorWithDynamicStateClonable(const std::string& s) : data(s) {}
+
+    using CloningFunctionType = stdx::function<std::unique_ptr<FunctorWithDynamicStateClonable>(
+        const FunctorWithDynamicStateClonable&)>;
+
+    static CloningFunctionType getCloningFunction() {
+        return [calls = 0](const FunctorWithDynamicStateClonable& c) mutable {
+            return mongo::stdx::make_unique<FunctorWithDynamicStateClonable>(
+                c.data + boost::lexical_cast<std::string>(++calls));
+        };
+    }
+};
+
+// This class models `Clonable`, with a return from clone which is
+// `Constructible<std::unique_ptr<RawPointerClonable>>` but isn't
+// `std::unique_ptr<RawPointerClonable>`.  This is used to test that the `clonable_ptr` class does
+// not expect `RawPointerClonable::clone() const` to return a model of
+// `UniquePtr<RawPointerClonable>`
+class RawPointerClonable {
+public:
+    RawPointerClonable* clone() const {
+        return new RawPointerClonable;
+    }
+};
+
+// This class models `Clonable`, with a return from clone which is
+// `Constructible<std::unique_ptr<UniquePtrClonable>>` because it is
+// `std::unique_ptr<UniquePtrClonable>`.  This is used to test that the `clonable_ptr` class can
+// use a `UniquePtrClonable::clone() const` that returns a model of
+// `UniquePtr<UniquePtrClonable>`
+class UniquePtrClonable {
+public:
+    std::unique_ptr<UniquePtrClonable> clone() const {
+        return mongo::stdx::make_unique<UniquePtrClonable>();
+    }
+};
+
+TEST(ClonablePtrTest, syntax_smoke_test) {
+// TODO: Either add a compressed pair type for optimization, or wait for MSVC to get this feature by
+//       default.  MSVC doesn't make its tuple compressed, which causes this test to fail on MSVC.
+#ifndef _MSC_VER
+    {
+        mongo::clonable_ptr<ClonableTest> p;
+
+        p = mongo::stdx::make_unique<ClonableTest>();
+
+        mongo::clonable_ptr<ClonableTest> p2 = p;
+
+        ASSERT_TRUE(p != p2);
+
+        static_assert(sizeof(p) == sizeof(ClonableTest*),
+                      "`mongo::clonable_ptr< T >` should be `sizeof` a pointer when there is no "
+                      "CloneFactory");
+    }
+#endif
+
+    {
+        mongo::clonable_ptr<AltClonableTest> p;
+
+        p = mongo::stdx::make_unique<AltClonableTest>();
+
+        mongo::clonable_ptr<AltClonableTest> p2 = p;
+
+        ASSERT_TRUE(p != p2);
+    }
+
+    {
+        mongo::clonable_ptr<Alt2ClonableTest> p;
+
+        p = mongo::stdx::make_unique<Alt2ClonableTest>();
+
+        mongo::clonable_ptr<Alt2ClonableTest> p2 = p;
+
+        ASSERT_TRUE(p != p2);
+    }
+
+    {
+        mongo::clonable_ptr<FunctorClonable, FunctorClonable::CloningFunctionType> p{
+            FunctorClonable::getCloningFunction()};
+
+        p = mongo::stdx::make_unique<FunctorClonable>();
+
+        mongo::clonable_ptr<FunctorClonable, FunctorClonable::CloningFunctionType> p2 = p;
+
+        ASSERT_TRUE(p != p2);
+
+        mongo::clonable_ptr<FunctorClonable, FunctorClonable::CloningFunctionType> p3{
+            FunctorClonable::getCloningFunction()};
+
+        auto tmp = mongo::stdx::make_unique<FunctorClonable>();
+        p3 = std::move(tmp);
+
+        ASSERT_TRUE(p != p2);
+        ASSERT_TRUE(p2 != p3);
+        ASSERT_TRUE(p != p3);
+    }
+}
+
+// These tests check that all expected valid syntactic forms of use for the
+// `mongo::clonable_ptr<Clonable>` are valid.  These tests assert nothing but provide a single
+// unified place to check the syntax of this component.  Build failures in these parts indicate that
+// a change to the component has broken an expected valid syntactic usage.  Any expected valid usage
+// which is not in this list should be added.
+namespace SyntaxTests {
+template <typename Clonable>
+void construction() {
+    // Test default construction
+    { mongo::clonable_ptr<Clonable>{}; }
+
+    // Test construction from a nullptr
+    { mongo::clonable_ptr<Clonable>{nullptr}; }
+
+    // Test construction from a Clonable pointer.
+    {
+        Clonable* const local = nullptr;
+        mongo::clonable_ptr<Clonable>{local};
+    }
+
+    // Test move construction.
+    { mongo::clonable_ptr<Clonable>{mongo::clonable_ptr<Clonable>{}}; }
+
+    // Test copy construction.
+    {
+        mongo::clonable_ptr<Clonable> a;
+        mongo::clonable_ptr<Clonable> b{a};
+    }
+
+    // Test move assignment.
+    {
+        mongo::clonable_ptr<Clonable> a;
+        a = mongo::clonable_ptr<Clonable>{};
+    }
+
+    // Test copy assignment.
+    {
+        mongo::clonable_ptr<Clonable> a;
+        mongo::clonable_ptr<Clonable> b;
+        b = a;
+    }
+
+    // Test unique pointer construction
+    { mongo::clonable_ptr<Clonable>{mongo::stdx::make_unique<Clonable>()}; }
+
+    // Test unique pointer construction (conversion)
+    {
+        auto acceptor = [](const mongo::clonable_ptr<Clonable>&) {};
+        acceptor(mongo::stdx::make_unique<Clonable>());
+    }
+
+    // Test non-conversion pointer construction
+    { static_assert(!std::is_convertible<Clonable*, mongo::clonable_ptr<Clonable>>::value, ""); }
+
+    // Test conversion unique pointer construction
+    {
+        static_assert(
+            std::is_convertible<std::unique_ptr<Clonable>, mongo::clonable_ptr<Clonable>>::value,
+            "");
+    }
+}
+
+// Tests that syntactic forms that require augmented construction are proper
+template <typename Clonable, typename CloneFactory>
+void augmentedConstruction() {
+    // Test default construction
+    {
+        static_assert(
+            !std::is_default_constructible<mongo::clonable_ptr<Clonable, CloneFactory>>::value, "");
+    }
+
+    // Test Clone Factory construction
+    { mongo::clonable_ptr<Clonable, CloneFactory>{Clonable::getCloningFunction()}; }
+
+// TODO: Revist this when MSVC's enable-if and deletion on ctors works.
+#ifndef _MSC_VER
+    // Test non-construction from a nullptr
+    {
+        static_assert(!std::is_constructible<mongo::clonable_ptr<Clonable, CloneFactory>,
+                                             std::nullptr_t>::value,
+                      "");
+    }
+#endif
+
+    // Test construction from a nullptr with factory
+    { mongo::clonable_ptr<Clonable, CloneFactory>{nullptr, Clonable::getCloningFunction()}; }
+
+// TODO: Revist this when MSVC's enable-if and deletion on ctors works.
+#ifndef _MSC_VER
+    // Test construction from a raw Clonable pointer.
+    {
+        static_assert(
+            !std::is_constructible<mongo::clonable_ptr<Clonable, CloneFactory>, Clonable*>::value,
+            "");
+    }
+#endif
+
+
+    // Test initialization of a raw Clonable pointer with factory, using reset.
+    {
+        Clonable* const local = nullptr;
+        mongo::clonable_ptr<Clonable, CloneFactory> p{Clonable::getCloningFunction()};
+        p.reset(local);
+    }
+
+    // Test move construction.
+    {
+        mongo::clonable_ptr<Clonable, CloneFactory>{
+            mongo::clonable_ptr<Clonable, CloneFactory>{Clonable::getCloningFunction()}};
+    }
+
+    // Test copy construction.
+    {
+        mongo::clonable_ptr<Clonable, CloneFactory> a{Clonable::getCloningFunction()};
+        mongo::clonable_ptr<Clonable, CloneFactory> b{a};
+    }
+
+    // Test augmented copy construction.
+    {
+        mongo::clonable_ptr<Clonable, CloneFactory> a{Clonable::getCloningFunction()};
+        mongo::clonable_ptr<Clonable, CloneFactory> b{a, Clonable::getCloningFunction()};
+    }
+
+
+    // Test move assignment.
+    {
+        mongo::clonable_ptr<Clonable, CloneFactory> a{Clonable::getCloningFunction()};
+        a = mongo::clonable_ptr<Clonable, CloneFactory>{Clonable::getCloningFunction()};
+    }
+
+    // Test copy assignment.
+    {
+        mongo::clonable_ptr<Clonable, CloneFactory> a{Clonable::getCloningFunction()};
+        mongo::clonable_ptr<Clonable, CloneFactory> b{Clonable::getCloningFunction()};
+        b = a;
+    }
+
+    // Test unique pointer construction
+    {
+        mongo::clonable_ptr<Clonable, CloneFactory>{mongo::stdx::make_unique<Clonable>(),
+                                                    Clonable::getCloningFunction()};
+    }
+
+    // Test augmented unique pointer construction
+    {
+        mongo::clonable_ptr<Clonable, CloneFactory>{mongo::stdx::make_unique<Clonable>(),
+                                                    Clonable::getCloningFunction()};
+    }
+
+    // Test non-conversion pointer construction
+    {
+        static_assert(
+            !std::is_convertible<mongo::clonable_ptr<Clonable, CloneFactory>, Clonable*>::value,
+            "");
+    }
+
+    // Test non-conversion from factory
+    {
+        static_assert(
+            !std::is_convertible<mongo::clonable_ptr<Clonable, CloneFactory>, CloneFactory>::value,
+            "");
+    }
+
+    // Test conversion unique pointer construction
+    {
+        static_assert(!std::is_convertible<std::unique_ptr<Clonable>,
+                                           mongo::clonable_ptr<Clonable, CloneFactory>>::value,
+                      "");
+    }
+}
+
+template <typename Clonable>
+void pointerOperations() {
+    mongo::clonable_ptr<Clonable> a;
+
+    // Test `.get()` functionality:
+    {
+        Clonable* p = a.get();
+        (void)p;
+    }
+
+    // Test `->` functionality
+    {
+        // We don't actually want to call the dtor, but we want the compiler to check that we
+        // have.
+        if (false) {
+            a->~Clonable();
+        }
+    }
+
+    // Test `*` functionality
+    {
+        Clonable& r = *a;
+        (void)r;
+    }
+
+    // Test reset functionality
+    {
+        a.reset();
+        a.reset(nullptr);
+        a.reset(new Clonable);
+    }
+}
+
+template <typename Clonable>
+void equalityOperations() {
+    mongo::clonable_ptr<Clonable> a;
+    mongo::clonable_ptr<Clonable> b;
+
+    std::unique_ptr<Clonable> ua;
+
+    // Test equality expressions
+    {
+        (void)(a == a);
+        (void)(a == b);
+        (void)(b == a);
+
+        (void)(a == ua);
+        (void)(ua == a);
+
+        (void)(nullptr == a);
+        (void)(a == nullptr);
+    }
+
+    // Test inequality expressions
+    {
+        (void)(a != a);
+        (void)(a != b);
+        (void)(b != a);
+
+        (void)(a != ua);
+        (void)(ua != a);
+
+        (void)(nullptr == a);
+        (void)(a == nullptr);
+    }
+}
+}  // namespace SyntaxTests
+
+TEST(ClonablePtrSyntaxTests, construction) {
+    SyntaxTests::construction<ClonableTest>();
+    SyntaxTests::construction<AltClonableTest>();
+    SyntaxTests::construction<Alt2ClonableTest>();
+    SyntaxTests::construction<RawPointerClonable>();
+    SyntaxTests::construction<UniquePtrClonable>();
+}
+
+TEST(ClonablePtrSyntaxTests, augmentedConstruction) {
+    SyntaxTests::augmentedConstruction<FunctorClonable, FunctorClonable::CloningFunctionType>();
+    SyntaxTests::augmentedConstruction<FunctorWithDynamicStateClonable,
+                                       FunctorWithDynamicStateClonable::CloningFunctionType>();
+}
+
+TEST(ClonablePtrSyntaxTests, pointerOperations) {
+    SyntaxTests::pointerOperations<ClonableTest>();
+    SyntaxTests::pointerOperations<AltClonableTest>();
+    SyntaxTests::pointerOperations<Alt2ClonableTest>();
+    SyntaxTests::pointerOperations<RawPointerClonable>();
+    SyntaxTests::pointerOperations<UniquePtrClonable>();
+}
+
+TEST(ClonablePtrSyntaxTests, equalityOperations) {
+    SyntaxTests::equalityOperations<ClonableTest>();
+    SyntaxTests::equalityOperations<AltClonableTest>();
+    SyntaxTests::equalityOperations<Alt2ClonableTest>();
+    SyntaxTests::equalityOperations<RawPointerClonable>();
+    SyntaxTests::equalityOperations<UniquePtrClonable>();
+}
+
+namespace BehaviorTests {
+class DetectDestruction {
+public:
+    static int activeCount;
+
+    static void resetCount() {
+        activeCount = 0;
+    }
+
+    ~DetectDestruction() {
+        --activeCount;
+    }
+
+    DetectDestruction(const DetectDestruction&) {
+        ++activeCount;
+    }
+
+    DetectDestruction& operator=(const DetectDestruction&) = delete;
+
+    DetectDestruction(DetectDestruction&&) = delete;
+    DetectDestruction& operator=(DetectDestruction&&) = delete;
+
+    DetectDestruction() {
+        ++activeCount;
+    }
+
+    std::unique_ptr<DetectDestruction> clone() const {
+        return mongo::stdx::make_unique<DetectDestruction>(*this);
+    }
+};
+
+int DetectDestruction::activeCount = 0;
+
+struct DestructionGuard {
+    DestructionGuard(const DestructionGuard&) = delete;
+    DestructionGuard& operator=(const DestructionGuard&) = delete;
+
+    DestructionGuard() {
+        DetectDestruction::resetCount();
+    }
+
+    ~DestructionGuard() {
+        ASSERT_EQ(DetectDestruction::activeCount, 0);
+    }
+};
+
+TEST(ClonablePtrTest, basic_construction_test) {
+    // Do not default construct the object
+    {
+        DestructionGuard check;
+        mongo::clonable_ptr<DetectDestruction> p;
+        ASSERT_EQ(DetectDestruction::activeCount, 0);
+    }
+
+    // Do not make unnecessary copies of the object from ptr
+    {
+        DestructionGuard check;
+        mongo::clonable_ptr<DetectDestruction> p{new DetectDestruction};
+        ASSERT_EQ(DetectDestruction::activeCount, 1);
+    }
+
+    // Do not make unnecessary copies of the object from unique_ptr
+    {
+        DestructionGuard check;
+        mongo::clonable_ptr<DetectDestruction> p{mongo::stdx::make_unique<DetectDestruction>()};
+        ASSERT_EQ(DetectDestruction::activeCount, 1);
+    }
+    {
+        DestructionGuard check;
+        mongo::clonable_ptr<DetectDestruction> p = mongo::stdx::make_unique<DetectDestruction>();
+        ASSERT_EQ(DetectDestruction::activeCount, 1);
+    }
+
+    // Two separate constructions are unlinked
+    {
+        DestructionGuard check;
+
+        mongo::clonable_ptr<DetectDestruction> p1{mongo::stdx::make_unique<DetectDestruction>()};
+        ASSERT_EQ(DetectDestruction::activeCount, 1);
+
+        {
+            mongo::clonable_ptr<DetectDestruction> p2{
+                mongo::stdx::make_unique<DetectDestruction>()};
+            ASSERT_EQ(DetectDestruction::activeCount, 2);
+        }
+        ASSERT_EQ(DetectDestruction::activeCount, 1);
+    }
+
+    // Two separate constructions can have opposite order and be unlinked
+    {
+        DestructionGuard check;
+
+        auto p1 = mongo::stdx::make_unique<mongo::clonable_ptr<DetectDestruction>>(
+            mongo::stdx::make_unique<DetectDestruction>());
+        ASSERT_EQ(DetectDestruction::activeCount, 1);
+
+        auto p2 = mongo::stdx::make_unique<mongo::clonable_ptr<DetectDestruction>>(
+            mongo::stdx::make_unique<DetectDestruction>());
+        ASSERT_EQ(DetectDestruction::activeCount, 2);
+
+        p1.reset();
+        ASSERT_EQ(DetectDestruction::activeCount, 1);
+
+        p2.reset();
+        ASSERT_EQ(DetectDestruction::activeCount, 0);
+    }
+}
+
+// TODO: Bring in an "equivalence class for equality predicate testing" framework.
+// Equals and Not Equals need to be tested independently -- It is not valid to assume that equals
+// and not equals are correctly implemented as complimentary predicates.  Equality must be
+// reflexive, symmetric and transitive.  This requres several instances that all have the same
+// value.  Simply testing "2 == 2" and "3 != 2" is insufficient.  Every combination of position and
+// equality must be tested to come out as expected.
+//
+// Consider that with equality it is important to make sure that `a == b` has the same meaning as `b
+// == a`.  It is also necessary to check that `a == b` and `b == c` and `a == c` is true, when all
+// three are equal, and to do so in reverse: `b == a` and `c == b` and `c == a`.  Further, the
+// relationships above have to hold for multiple cases.  Similar cases need to be tested for
+// inequality.
+//
+// Further, equality is an incredibly important operation to test completely and thoroughly --
+// besides being a critical element in code using any value modeling type, it also is the keystone
+// in any testing schedule for a copyable and movable value type.  Almost all testing of behavior
+// relies upon being able to detect fundamental differences in value.  In order to provide this
+// correctly, we provide a full battery of tests for equality in all mathematically relevant
+// situations.  For this equality testing schedule to be correct, we require a mechanism to
+// initialize objects (and references to those objects) which have predictable value.  These
+// predictable values are then used to test known equality expressions for the correct evaluation.
+//
+// All other tests can then just use equality to verify that an object is in the desired state.
+// This greatly simplifies testing and also makes tests more precise.
+TEST(ClonablePtrTest, basicEqualityTest) {
+    DestructionGuard check;
+
+    mongo::clonable_ptr<DetectDestruction> n1;
+    mongo::clonable_ptr<DetectDestruction> n2;
+    mongo::clonable_ptr<DetectDestruction> n3;
+
+    mongo::clonable_ptr<DetectDestruction> a = mongo::stdx::make_unique<DetectDestruction>();
+    mongo::clonable_ptr<DetectDestruction> b = mongo::stdx::make_unique<DetectDestruction>();
+    mongo::clonable_ptr<DetectDestruction> c = mongo::stdx::make_unique<DetectDestruction>();
+
+    const mongo::clonable_ptr<DetectDestruction>& ap = a;
+    const mongo::clonable_ptr<DetectDestruction>& bp = b;
+    const mongo::clonable_ptr<DetectDestruction>& cp = c;
+    const mongo::clonable_ptr<DetectDestruction>& ap2 = a;
+    const mongo::clonable_ptr<DetectDestruction>& bp2 = b;
+    const mongo::clonable_ptr<DetectDestruction>& cp2 = c;
+
+    // Equals operator
+
+    // Identity checks
+
+    ASSERT(n1 == n1);
+    ASSERT(n2 == n2);
+    ASSERT(n3 == n3);
+
+    ASSERT(a == a);
+    ASSERT(b == b);
+    ASSERT(c == c);
+
+    // Same value checks.  (Because unique pointers should never be the same value, we have to use
+    // references.)
+
+    ASSERT(n1 == n2);
+    ASSERT(n1 == n3);
+
+    ASSERT(n2 == n1);
+    ASSERT(n2 == n3);
+
+    ASSERT(n3 == n1);
+    ASSERT(n3 == n2);
+
+    ASSERT(a == ap);
+    ASSERT(a == ap2);
+    ASSERT(ap == a);
+    ASSERT(ap == ap2);
+    ASSERT(ap2 == a);
+    ASSERT(ap2 == ap);
+
+    ASSERT(b == bp);
+    ASSERT(b == bp2);
+    ASSERT(bp == b);
+    ASSERT(bp == bp2);
+    ASSERT(bp2 == b);
+    ASSERT(bp2 == bp);
+
+    ASSERT(c == cp);
+    ASSERT(c == cp2);
+    ASSERT(cp == c);
+    ASSERT(cp == cp2);
+    ASSERT(cp2 == c);
+    ASSERT(cp2 == cp);
+
+    // Different value checks:
+
+    ASSERT(!(a == n1));
+    ASSERT(!(b == n1));
+    ASSERT(!(c == n1));
+    ASSERT(!(a == n2));
+    ASSERT(!(b == n2));
+    ASSERT(!(c == n2));
+
+    ASSERT(!(n1 == a));
+    ASSERT(!(n1 == b));
+    ASSERT(!(n1 == c));
+    ASSERT(!(n2 == a));
+    ASSERT(!(n2 == b));
+    ASSERT(!(n2 == c));
+
+    ASSERT(!(a == b));
+    ASSERT(!(a == c));
+
+    ASSERT(!(b == a));
+    ASSERT(!(b == c));
+
+    ASSERT(!(c == a));
+    ASSERT(!(c == b));
+
+    // Not Equals operator
+
+    // Identity checks
+
+    ASSERT(!(n1 != n1));
+    ASSERT(!(n2 != n2));
+    ASSERT(!(n3 != n3));
+
+    ASSERT(!(a != a));
+    ASSERT(!(b != b));
+    ASSERT(!(c != c));
+
+    // Same value checks.  (Because unique pointers should never be the same value, we have to use
+    // references.)
+
+    ASSERT(!(n1 != n2));
+    ASSERT(!(n1 != n3));
+
+    ASSERT(!(n2 != n1));
+    ASSERT(!(n2 != n3));
+
+    ASSERT(!(n3 != n1));
+    ASSERT(!(n3 != n2));
+
+    ASSERT(!(a != ap));
+    ASSERT(!(a != ap2));
+    ASSERT(!(ap != a));
+    ASSERT(!(ap != ap2));
+    ASSERT(!(ap2 != a));
+    ASSERT(!(ap2 != ap));
+
+    ASSERT(!(b != bp));
+    ASSERT(!(b != bp2));
+    ASSERT(!(bp != b));
+    ASSERT(!(bp != bp2));
+    ASSERT(!(bp2 != b));
+    ASSERT(!(bp2 != bp));
+
+    ASSERT(!(c != cp));
+    ASSERT(!(c != cp2));
+    ASSERT(!(cp != c));
+    ASSERT(!(cp != cp2));
+    ASSERT(!(cp2 != c));
+    ASSERT(!(cp2 != cp));
+
+    // Different value checks:
+
+    ASSERT(a != n1);
+    ASSERT(b != n1);
+    ASSERT(c != n1);
+    ASSERT(a != n2);
+    ASSERT(b != n2);
+    ASSERT(c != n2);
+
+    ASSERT(n1 != a);
+    ASSERT(n1 != b);
+    ASSERT(n1 != c);
+    ASSERT(n2 != a);
+    ASSERT(n2 != b);
+    ASSERT(n2 != c);
+
+    ASSERT(a != b);
+    ASSERT(a != c);
+
+    ASSERT(b != a);
+    ASSERT(b != c);
+
+    ASSERT(c != a);
+    ASSERT(c != b);
+}
+
+// TODO: all other forms of equality with other types (`std::nullptr_t` and `std::unique_ptr< T >`)
+// need testing still.
+
+TEST(ClonablePtrTest, ownershipStabilityTest) {
+    {
+        DestructionGuard check;
+
+        auto ptr_init = mongo::stdx::make_unique<DetectDestruction>();
+        const auto* rp = ptr_init.get();
+
+        mongo::clonable_ptr<DetectDestruction> cp = std::move(ptr_init);
+
+        ASSERT(rp == cp.get());
+
+        mongo::clonable_ptr<DetectDestruction> cp2 = std::move(cp);
+
+        ASSERT(rp == cp2.get());
+
+        mongo::clonable_ptr<DetectDestruction> cp3;
+
+        ASSERT(nullptr == cp3);
+
+        cp3 = std::move(cp2);
+
+        ASSERT(rp == cp3.get());
+    }
+
+    {
+        auto ptr_init = mongo::stdx::make_unique<DetectDestruction>();
+        const auto* rp = ptr_init.get();
+
+        mongo::clonable_ptr<DetectDestruction> cp{ptr_init.release()};
+
+        ASSERT(rp == cp.get());
+
+        mongo::clonable_ptr<DetectDestruction> cp2 = std::move(cp);
+
+        ASSERT(rp == cp2.get());
+
+        mongo::clonable_ptr<DetectDestruction> cp3;
+
+        ASSERT(nullptr == cp3.get());
+
+        cp3 = std::move(cp2);
+
+        ASSERT(rp == cp3.get());
+    }
+}
+
+class ClonableObject {
+private:
+    int value = 0;
+
+public:
+    // ClonableObject( const ClonableObject & ) { abort(); }
+    ClonableObject() = default;
+    explicit ClonableObject(const int v) : value(v) {}
+
+    std::unique_ptr<ClonableObject> clone() const {
+        return mongo::stdx::make_unique<ClonableObject>(*this);
+    }
+
+    auto make_equality_lens() const -> decltype(std::tie(this->value)) {
+        return std::tie(value);
+    }
+};
+
+bool operator==(const ClonableObject& lhs, const ClonableObject& rhs) {
+    return lhs.make_equality_lens() == rhs.make_equality_lens();
+}
+
+bool operator!=(const ClonableObject& lhs, const ClonableObject& rhs) {
+    return !(lhs == rhs);
+}
+
+TEST(ClonablePtrTest, noObjectCopySemanticTest) {
+    mongo::clonable_ptr<ClonableObject> p;
+
+    mongo::clonable_ptr<ClonableObject> p2 = p;
+    ASSERT(p == p2);
+
+    mongo::clonable_ptr<ClonableObject> p3;
+
+    p3 = p;
+    ASSERT(p == p3);
+}
+
+TEST(ClonablePtrTest, objectCopySemanticTest) {
+    mongo::clonable_ptr<ClonableObject> p = mongo::stdx::make_unique<ClonableObject>(1);
+    mongo::clonable_ptr<ClonableObject> q = mongo::stdx::make_unique<ClonableObject>(2);
+    ASSERT(p != q);
+    ASSERT(*p != *q);
+
+    mongo::clonable_ptr<ClonableObject> p2 = p;
+    ASSERT(p != p2);
+    ASSERT(*p == *p2);
+
+    mongo::clonable_ptr<ClonableObject> q2 = q;
+    ASSERT(q2 != q);
+    ASSERT(q2 != p);
+    ASSERT(q2 != p2);
+    ASSERT(*q2 == *q);
+
+    q2 = p2;
+    ASSERT(q2 != q);
+    ASSERT(q2 != p);
+    ASSERT(q2 != p2);
+    ASSERT(*q2 == *p2);
+}
+
+class Interface {
+public:
+    virtual ~Interface() = default;
+    virtual void consumeText(const std::string& message) = 0;
+    virtual std::string produceText() = 0;
+
+    std::unique_ptr<Interface> clone() const {
+        return std::unique_ptr<Interface>{this->clone_impl()};
+    }
+
+private:
+    virtual Interface* clone_impl() const = 0;
+};
+
+class GeneratorImplementation : public Interface {
+private:
+    const std::string root;
+    int generation = 0;
+
+    GeneratorImplementation* clone_impl() const {
+        return new GeneratorImplementation{*this};
+    }
+
+public:
+    explicit GeneratorImplementation(const std::string& m) : root(m) {}
+
+    void consumeText(const std::string&) override {}
+
+    std::string produceText() override {
+        return root + boost::lexical_cast<std::string>(++generation);
+    }
+};
+
+class StorageImplementation : public Interface {
+private:
+    std::string store;
+
+    StorageImplementation* clone_impl() const {
+        return new StorageImplementation{*this};
+    }
+
+public:
+    void consumeText(const std::string& m) override {
+        store = m;
+    }
+    std::string produceText() override {
+        return store;
+    }
+};
+
+
+TEST(ClonablePtrSimpleTest, simpleUsageExample) {
+    mongo::clonable_ptr<Interface> source;
+    mongo::clonable_ptr<Interface> sink;
+
+    mongo::clonable_ptr<Interface> instance = stdx::make_unique<StorageImplementation>();
+
+    sink = instance;
+
+    ASSERT(instance.get() != sink.get());
+
+    instance = stdx::make_unique<GeneratorImplementation>("base message");
+
+
+    source = std::move(instance);
+
+
+    sink->consumeText(source->produceText());
+}
+
+}  // namespace BehaviorTests
+}  // namespace
diff --git a/src/mongo/base/concept/README b/src/mongo/base/concept/README
new file mode 100644
index 00000000000..bc2c74fabe4
--- /dev/null
+++ b/src/mongo/base/concept/README
@@ -0,0 +1,5 @@
+This directory contains a number of C++ headers which describe concepts for
+C++ types used by and with the Mongo library.  These headers do not describe
+instantiable types, but instead are used to concisely describe models of C++
+type concepts.  When C++ grows a proper `Concepts` feature, these files can be
+converted to proper concepts.
diff --git a/src/mongo/base/concept/assignable.h b/src/mongo/base/concept/assignable.h
new file mode 100644
index 00000000000..00a8fbfad1e
--- /dev/null
+++ b/src/mongo/base/concept/assignable.h
@@ -0,0 +1,40 @@
+/*-
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects
+ *    for all of the code used other than as permitted herein. If you modify
+ *    file(s) with this exception, you may extend this exception to your
+ *    version of the file(s), but you are not obligated to do so. If you do not
+ *    wish to do so, delete this exception statement from your version. If you
+ *    delete this exception statement from all source files in the program,
+ *    then also delete it in the license file.
+ */
+#pragma once
+
+#include "mongo/base/concept/copy_assignable.h"
+#include "mongo/base/concept/copy_constructible.h"
+
+namespace mongo {
+namespace concept {
+/*!
+ * The Assignable concept models a type which can be copy assigned and copy constructed.
+ */
+struct Assignable : CopyConstructible, CopyAssignable {};
+}  // namespace concept
+}  // namespace mongo
diff --git a/src/mongo/base/concept/clonable.h b/src/mongo/base/concept/clonable.h
new file mode 100644
index 00000000000..71bd3590b33
--- /dev/null
+++ b/src/mongo/base/concept/clonable.h
@@ -0,0 +1,47 @@
+/*-
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects
+ *    for all of the code used other than as permitted herein. If you modify
+ *    file(s) with this exception, you may extend this exception to your
+ *    version of the file(s), but you are not obligated to do so. If you do not
+ *    wish to do so, delete this exception statement from your version. If you
+ *    delete this exception statement from all source files in the program,
+ *    then also delete it in the license file.
+ */
+#pragma once
+
+#include "mongo/base/concept/constructible.h"
+#include "mongo/base/concept/unique_ptr.h"
+
+namespace mongo {
+namespace concept {
+/*!
+ * Objects conforming to the Clonable concept can be dynamically copied, using `this->clone()`.
+ * The Clonable concept does not specify the return type of the `clone()` function.
+ */
+struct Clonable {
+    /*! Clonable objects must be safe to destroy, by pointer. */
+    virtual ~Clonable() noexcept = 0;
+
+    /*! Clonable objects can be cloned without knowing the actual dynamic type. */
+    Constructible<UniquePtr<Clonable>> clone() const;
+};
+}  // namespace concept
+}  // namespace mongo
diff --git a/src/mongo/base/concept/clone_factory.h b/src/mongo/base/concept/clone_factory.h
new file mode 100644
index 00000000000..ae330ade081
--- /dev/null
+++ b/src/mongo/base/concept/clone_factory.h
@@ -0,0 +1,48 @@
+/*-
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects
+ *    for all of the code used other than as permitted herein. If you modify
+ *    file(s) with this exception, you may extend this exception to your
+ *    version of the file(s), but you are not obligated to do so. If you do not
+ *    wish to do so, delete this exception statement from your version. If you
+ *    delete this exception statement from all source files in the program,
+ *    then also delete it in the license file.
+ */
+#pragma once
+
+#include "mongo/base/concept/assignable.h"
+#include "mongo/base/concept/constructible.h"
+#include "mongo/base/concept/unique_ptr.h"
+
+namespace mongo {
+namespace concept {
+/*!
+ * Objects conforming to the `CloneFactory` concept are function-like constructs which return
+ * objects that are dynamically allocated copies of their inputs.
+ * These copies can be made without knowing the actual dynamic type.  The `CloneFactory` type itself
+ * must be `Assignable`, in that it can be used with automatically generated copy constructors and
+ * copy assignment operators.
+ */
+template <typename T>
+struct CloneFactory : Assignable {
+    Constructible<UniquePtr<T>> operator()(const T*) const;
+};
+}  // namespace concept
+}  // namespace mongo
diff --git a/src/mongo/base/concept/constructible.h b/src/mongo/base/concept/constructible.h
new file mode 100644
index 00000000000..d857efdd292
--- /dev/null
+++ b/src/mongo/base/concept/constructible.h
@@ -0,0 +1,65 @@
+/*-
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects
+ *    for all of the code used other than as permitted herein. If you modify
+ *    file(s) with this exception, you may extend this exception to your
+ *    version of the file(s), but you are not obligated to do so. If you do not
+ *    wish to do so, delete this exception statement from your version. If you
+ *    delete this exception statement from all source files in the program,
+ *    then also delete it in the license file.
+ */
+#pragma once
+
+#include <type_traits>
+
+#include "mongo/stdx/type_traits.h"
+
+namespace mongo {
+namespace concept {
+
+/**
+ * The Constructable trait indicates whether `T` is constructible from `Constructible`.
+ *
+ * RETURNS: true if `T{ std::declval< Constructible >() }` is a valid expression and false
+ * otherwise.
+ */
+template <typename T, typename Constructible, typename = void>
+struct is_constructible : std::false_type {};
+
+template <typename T, typename Constructible>
+struct is_constructible<T,
+                        Constructible,
+                        stdx::void_t<decltype(T{std::declval<Constructible<T>>()})>>
+    : std::true_type {};
+
+/**
+ * The Constructable concept models a type which can be passed to a single-argument constructor of
+ * `T`.
+ * This is not possible to describe in the type `Constructible`.
+ *
+ * The expression: `T{ std::declval< Constructible< T > >() }` should be valid.
+ *
+ * This concept is more broadly applicable than `ConvertibleTo`.  `ConvertibleTo` uses implicit
+ * conversion, whereas `Constructible` uses direct construction.
+ */
+template <typename T>
+struct Constructible {};
+}  // namespace concept
+}  // namespace mongo
diff --git a/src/mongo/base/concept/convertible_to.h b/src/mongo/base/concept/convertible_to.h
new file mode 100644
index 00000000000..ca907d86a57
--- /dev/null
+++ b/src/mongo/base/concept/convertible_to.h
@@ -0,0 +1,41 @@
+/*-
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects
+ *    for all of the code used other than as permitted herein. If you modify
+ *    file(s) with this exception, you may extend this exception to your
+ *    version of the file(s), but you are not obligated to do so. If you do not
+ *    wish to do so, delete this exception statement from your version. If you
+ *    delete this exception statement from all source files in the program,
+ *    then also delete it in the license file.
+ */
+#pragma once
+
+namespace mongo {
+namespace concept {
+/**
+ * The ConvertibleTo concept models a type which can be converted implicitly into a `T`.
+ * The code: `T x; x= ConvertibleTo< T >{};` should be valid.
+ */
+template <typename T>
+struct ConvertibleTo {
+    operator T();
+}
+}  // namespace concept
+}  // namespace mongo
diff --git a/src/mongo/base/concept/copy_assignable.h b/src/mongo/base/concept/copy_assignable.h
new file mode 100644
index 00000000000..e46e2c7af18
--- /dev/null
+++ b/src/mongo/base/concept/copy_assignable.h
@@ -0,0 +1,45 @@
+/*-
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects
+ *    for all of the code used other than as permitted herein. If you modify
+ *    file(s) with this exception, you may extend this exception to your
+ *    version of the file(s), but you are not obligated to do so. If you do not
+ *    wish to do so, delete this exception statement from your version. If you
+ *    delete this exception statement from all source files in the program,
+ *    then also delete it in the license file.
+ */
+#pragma once
+
+namespace mongo {
+namespace concept {
+/**
+ * The CopyAssignable concept models a type which can be copy assigned.
+ *
+ * The expression: `copyAssignable= copyAssignable` should be valid.
+ */
+struct CopyAssignable {
+    /**
+     * The copy assignment operator is required by `CopyAssignable`.
+     * NOTE: Copy Assignment is only required on lvalue targets of `CopyAssignable`.
+     */
+    CopyAssignable& operator=(const CopyAssignable&) &;
+};
+}  // namespace concept
+}  // namespace mongo
diff --git a/src/mongo/base/concept/copy_constructible.h b/src/mongo/base/concept/copy_constructible.h
new file mode 100644
index 00000000000..e2850c70384
--- /dev/null
+++ b/src/mongo/base/concept/copy_constructible.h
@@ -0,0 +1,41 @@
+/*-
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects
+ *    for all of the code used other than as permitted herein. If you modify
+ *    file(s) with this exception, you may extend this exception to your
+ *    version of the file(s), but you are not obligated to do so. If you do not
+ *    wish to do so, delete this exception statement from your version. If you
+ *    delete this exception statement from all source files in the program,
+ *    then also delete it in the license file.
+ */
+#pragma once
+
+namespace mongo {
+namespace concept {
+/**
+ * The CopyConstructable concept models a type which can be copy constructed.
+ *
+ * The expression: `CopyConstructible{ copyConstructible }` should be valid.
+ */
+struct CopyConstructible {
+    CopyConstructible(const CopyConstructible&);
+};
+}  // namespace concept
+}  // namespace mongo
diff --git a/src/mongo/base/concept/unique_ptr.h b/src/mongo/base/concept/unique_ptr.h
new file mode 100644
index 00000000000..13ca5495e44
--- /dev/null
+++ b/src/mongo/base/concept/unique_ptr.h
@@ -0,0 +1,68 @@
+/*-
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects
+ *    for all of the code used other than as permitted herein. If you modify
+ *    file(s) with this exception, you may extend this exception to your
+ *    version of the file(s), but you are not obligated to do so. If you do not
+ *    wish to do so, delete this exception statement from your version. If you
+ *    delete this exception statement from all source files in the program,
+ *    then also delete it in the license file.
+ */
+#pragma once
+
+#include "mongo/base/concept/convertible_to.h"
+
+namespace mongo {
+namespace concept {
+/**
+ * The `UniquePtr` Concept models a movable owning pointer of an object.
+ * `std::unique_ptr< T >` is a model of `mongo::concept::UniquePtr< T >`.
+ */
+template <typename T>
+struct UniquePtr {
+    /** The `UniquePtr< T >` must retire its pointer to `T` on destruction. */
+    ~UniquePtr() noexcept;
+
+    UniquePtr(UniquePtr&& p);
+    UniquePtr& operator=(UniquePtr&& p);
+
+    UniquePtr();
+    UniquePtr(T* p);
+
+    ConvertibleTo<T*> operator->() const;
+    T& operator*() const;
+
+    explicit operator bool() const;
+
+    ConvertibleTo<T*> get() const;
+
+    void reset() noexcept;
+    void reset(ConvertibleTo<T*>);
+};
+
+/*! A `UniquePtr` object must be equality comparable. */
+template <typename T>
+bool operator==(const UniquePtr<T>& lhs, const UniquePtr<T>& rhs);
+
+/*! A `UniquePtr` object must be inequality comparable. */
+template <typename T>
+bool operator!=(const UniquePtr<T>& lhs, const UniquePtr<T>& rhs);
+}  // namespace concept
+}  // namespace mongo