d

v4/any.h

@@ -0,0 +1,549 @@
+/**
+ * Implementation of N4562 std::experimental::any (merged into C++17 as std::any)
+ * for C++11 compilers.
+ *
+ * See also:
+ *   + http://en.cppreference.com/w/cpp/any
+ *   + http://en.cppreference.com/w/cpp/experimental/any
+ *   + http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4562.html#any
+ *   + https://cplusplus.github.io/LWG/lwg-active.html#2509
+ *
+ * Copyright (c) 2016 Denilson das Mercês Amorim
+ * Copyright (c) 2018 Claudio Fantacci
+ *
+ * Distributed under the Boost Software License, Version 1.0.
+ * (See accompanying file LICENSE.md or copy at http://www.boost.org/LICENSE_1_0.txt)
+ */
+
+#ifndef ANY_H
+#define ANY_H
+
+#include <stdexcept>
+#include <typeinfo>
+#include <type_traits>
+
+
+namespace libany
+{
+
+class bad_any_cast : public std::bad_cast
+{
+public:
+    const char* what() const noexcept override
+    {
+        return "bad any_cast";
+    }
+};
+
+
+class any final
+{
+public:
+    /**
+     * Constructs an object of type any with an empty state.
+     */
+    any() :
+        vtable(nullptr)
+    { }
+
+
+    /**
+     * Constructs an object of type any with an equivalent state as other.
+     */
+    any(const any& rhs) :
+        vtable(rhs.vtable)
+    {
+        if(rhs.has_value())
+        {
+            rhs.vtable->copy(rhs.storage, this->storage);
+        }
+    }
+
+
+    /**
+     * Constructs an object of type any with a state equivalent to the original state of other.
+     * rhs is left in a valid but otherwise unspecified state.
+     */
+    any(any&& rhs) noexcept :
+        vtable(rhs.vtable)
+    {
+        if(rhs.has_value())
+        {
+            rhs.vtable->move(rhs.storage, this->storage);
+            rhs.vtable = nullptr;
+        }
+    }
+
+
+    /**
+     * Same effect as this->clear().
+     */
+    ~any()
+    {
+        this->reset();
+    }
+
+
+    /**
+     * Constructs an object of type any that contains an object of type T direct-initialized with std::forward<ValueType>(value).
+     * T shall satisfy the CopyConstructible requirements, otherwise the program is ill-formed.
+     * This is because an `any` may be copy constructed into another `any` at any time, so a copy should always be allowed.
+     */
+    template<typename ValueType, typename = typename std::enable_if<!std::is_same<typename std::decay<ValueType>::type, any>::value>::type>
+    any(ValueType&& value)
+    {
+        static_assert(std::is_copy_constructible<typename std::decay<ValueType>::type>::value,
+                      "T shall satisfy the CopyConstructible requirements.");
+        this->construct(std::forward<ValueType>(value));
+    }
+
+
+    /**
+     * Has the same effect as any(rhs).swap(*this). No effects if an exception is thrown.
+     */
+    any& operator=(const any& rhs)
+    {
+        any(rhs).swap(*this);
+        return *this;
+    }
+
+
+    /**
+     * Has the same effect as any(std::move(rhs)).swap(*this).
+     * The state of *this is equivalent to the original state of rhs and rhs is left in a valid
+     * but otherwise unspecified state.
+     */
+    any& operator=(any&& rhs) noexcept
+    {
+        any(std::move(rhs)).swap(*this);
+        return *this;
+    }
+
+
+    /**
+     * Has the same effect as any(std::forward<ValueType>(value)).swap(*this). No effect if a exception is thrown.
+     * T shall satisfy the CopyConstructible requirements, otherwise the program is ill-formed.
+     * This is because an `any` may be copy constructed into another `any` at any time, so a copy should always be allowed.
+     */
+    template<typename ValueType, typename = typename std::enable_if<!std::is_same<typename std::decay<ValueType>::type, any>::value>::type>
+    any& operator=(ValueType&& value)
+    {
+        static_assert(std::is_copy_constructible<typename std::decay<ValueType>::type>::value, "T shall satisfy the CopyConstructible requirements.");
+        any(std::forward<ValueType>(value)).swap(*this);
+        return *this;
+    }
+
+
+    /**
+     * If not empty, destroys the contained object.
+     */
+    void reset() noexcept
+    {
+        if(has_value())
+        {
+            this->vtable->destroy(storage);
+            this->vtable = nullptr;
+        }
+    }
+
+
+    /**
+     * Returns true if *this has no contained object, otherwise false.
+     */
+    bool has_value() const noexcept
+    {
+        return this->vtable != nullptr;
+    }
+
+
+    /**
+     * If *this has a contained object of type T, typeid(T); otherwise typeid(void).
+     */
+    const std::type_info& type() const noexcept
+    {
+        return has_value()? this->vtable->type() : typeid(void);
+    }
+
+
+    /**
+     * Exchange the states of *this and rhs.
+     */
+    void swap(any& other) noexcept
+    {
+        if(this->vtable != other.vtable)
+        {
+            any tmp(std::move(other));
+
+            other.vtable = this->vtable;
+            if(this->vtable != nullptr)
+                this->vtable->move(this->storage, other.storage);
+
+            this->vtable = tmp.vtable;
+            if(tmp.vtable != nullptr)
+            {
+                tmp.vtable->move(tmp.storage, this->storage);
+                tmp.vtable = nullptr;
+            }
+        }
+        else
+        {
+            if(this->vtable != nullptr)
+                this->vtable->swap(this->storage, other.storage);
+        }
+    }
+
+
+private:
+    union storage_union
+    {
+        using stack_storage_t = typename std::aligned_storage<2 * sizeof(void*), std::alignment_of<void*>::value>::type;
+
+        void* dynamic;
+
+        stack_storage_t stack;
+    };
+
+
+    /**
+     * Base VTable specification.
+     *
+     * Note: The caller is responsible for doing .vtable = nullptr after destructful operations
+     * such as destroy() and/or move().
+     */
+    struct vtable_type
+    {
+        /**
+         * The type of the object this vtable is for.
+         */
+        const std::type_info& (*type)() noexcept;
+
+
+        /**
+         * Destroys the object in the union.
+         * The state of the union after this call is unspecified, caller must ensure not to use src anymore.
+         */
+        void(*destroy)(storage_union&) noexcept;
+
+
+        /**
+         * Copies the **inner** content of the src union into the yet unitialized dest union.
+         * As such, both inner objects will have the same state, but on separate memory locations.
+         */
+        void(*copy)(const storage_union& src, storage_union& dest);
+
+
+        /**
+         * Moves the storage from src to the yet unitialized dest union.
+         * The state of src after this call is unspecified, caller must ensure not to use src anymore.
+         */
+        void(*move)(storage_union& src, storage_union& dest) noexcept;
+
+
+        /**
+         * Exchanges the storage between lhs and rhs.
+         */
+        void(*swap)(storage_union& lhs, storage_union& rhs) noexcept;
+    };
+
+
+    /**
+     * VTable for dynamically allocated storage.
+     */
+    template<typename T>
+    struct vtable_dynamic
+    {
+        static const std::type_info& type() noexcept
+        {
+            return typeid(T);
+        }
+
+
+        static void destroy(storage_union& storage) noexcept
+        {
+            delete reinterpret_cast<T*>(storage.dynamic);
+        }
+
+
+        static void copy(const storage_union& src, storage_union& dest)
+        {
+            dest.dynamic = new T(*reinterpret_cast<const T*>(src.dynamic));
+        }
+
+
+        static void move(storage_union& src, storage_union& dest) noexcept
+        {
+            dest.dynamic = src.dynamic;
+            src.dynamic = nullptr;
+        }
+
+
+        static void swap(storage_union& lhs, storage_union& rhs) noexcept
+        {
+            std::swap(lhs.dynamic, rhs.dynamic);
+        }
+    };
+
+
+    /**
+     * VTable for stack allocated storage.
+     */
+    template<typename T>
+    struct vtable_stack
+    {
+        static const std::type_info& type() noexcept
+        {
+            return typeid(T);
+        }
+
+
+        static void destroy(storage_union& storage) noexcept
+        {
+            reinterpret_cast<T*>(&storage.stack)->~T();
+        }
+
+
+        static void copy(const storage_union& src, storage_union& dest)
+        {
+            new (&dest.stack) T(reinterpret_cast<const T&>(src.stack));
+        }
+
+
+        static void move(storage_union& src, storage_union& dest) noexcept
+        {
+            /**
+             * One of the conditions for using vtable_stack is a nothrow move constructor,
+             * so this move constructor will never throw a exception.
+             */
+            new (&dest.stack) T(std::move(reinterpret_cast<T&>(src.stack)));
+            destroy(src);
+        }
+
+
+        static void swap(storage_union& lhs, storage_union& rhs) noexcept
+        {
+            storage_union tmp_storage;
+            move(rhs, tmp_storage);
+            move(lhs, rhs);
+            move(tmp_storage, lhs);
+        }
+    };
+
+
+    /**
+     * Whether the type T must be dynamically allocated or can be stored on the stack.
+     */
+    template<typename T>
+    struct requires_allocation :
+        std::integral_constant<bool, !(std::is_nothrow_move_constructible<T>::value // N4562 6.3/3 [any.class]
+                                       && sizeof(T) <= sizeof(storage_union::stack)
+                                       && std::alignment_of<T>::value <= std::alignment_of<storage_union::stack_storage_t>::value)>
+    { };
+
+
+    /**
+     * Returns the pointer to the vtable of the type T.
+     */
+    template<typename T>
+    static vtable_type* vtable_for_type()
+    {
+        using VTableType = typename std::conditional<requires_allocation<T>::value, vtable_dynamic<T>, vtable_stack<T>>::type;
+        static vtable_type table = { VTableType::type, VTableType::destroy, VTableType::copy, VTableType::move, VTableType::swap };
+        return &table;
+    }
+
+
+protected:
+    template<typename T>
+    friend const T* any_cast(const any* operand) noexcept;
+
+
+    template<typename T>
+    friend T* any_cast(any* operand) noexcept;
+
+
+    /**
+     * Same effect as is_same(this->type(), t);
+     */
+    bool is_typed(const std::type_info& t) const
+    {
+        return is_same(this->type(), t);
+    }
+
+
+    /**
+     * Checks if two type infos are the same.
+     * If ANY_IMPL_FAST_TYPE_INFO_COMPARE is defined, checks only the address of the
+     * type infos, otherwise does an actual comparision. Checking addresses is
+     * only a valid approach when there's no interaction with outside sources
+     * (other shared libraries and such).
+     */
+    static bool is_same(const std::type_info& a, const std::type_info& b)
+    {
+#ifdef ANY_IMPL_FAST_TYPE_INFO_COMPARE
+        return &a == &b;
+#else
+        return a == b;
+#endif
+    }
+
+
+    /**
+     * Casts (with no type_info checks) the storage pointer as const T*.
+     */
+    template<typename T>
+    const T* cast() const noexcept
+    {
+        return requires_allocation<typename std::decay<T>::type>::value ? reinterpret_cast<const T*>(storage.dynamic) : reinterpret_cast<const T*>(&storage.stack);
+    }
+
+
+    /**
+     * Casts (with no type_info checks) the storage pointer as T*.
+     */
+    template<typename T>
+    T* cast() noexcept
+    {
+        return requires_allocation<typename std::decay<T>::type>::value ? reinterpret_cast<T*>(storage.dynamic) : reinterpret_cast<T*>(&storage.stack);
+    }
+
+
+private:
+    storage_union storage; // On offset(0) so no padding for align
+
+    vtable_type* vtable;
+
+
+    template<typename ValueType, typename T>
+    typename std::enable_if<requires_allocation<T>::value>::type do_construct(ValueType&& value)
+    {
+        storage.dynamic = new T(std::forward<ValueType>(value));
+    }
+
+
+    template<typename ValueType, typename T>
+    typename std::enable_if<!requires_allocation<T>::value>::type do_construct(ValueType&& value)
+    {
+        new (&storage.stack) T(std::forward<ValueType>(value));
+    }
+
+
+    /**
+     * Chooses between stack and dynamic allocation for the type decay_t<ValueType>,
+     * assigns the correct vtable, and constructs the object on our storage.
+     */
+    template<typename ValueType>
+    void construct(ValueType&& value)
+    {
+        using T = typename std::decay<ValueType>::type;
+
+        this->vtable = vtable_for_type<T>();
+
+        do_construct<ValueType,T>(std::forward<ValueType>(value));
+    }
+};
+
+
+namespace detail
+{
+    template<typename ValueType>
+    inline ValueType any_cast_move_if_true(typename std::remove_reference<ValueType>::type* p, std::true_type)
+    {
+        return std::move(*p);
+    }
+
+
+    template<typename ValueType>
+    inline ValueType any_cast_move_if_true(typename std::remove_reference<ValueType>::type* p, std::false_type)
+    {
+        return *p;
+    }
+}
+
+
+/**
+ * Performs *any_cast<add_const_t<remove_reference_t<ValueType>>>(&operand), or throws bad_any_cast on failure.
+ */
+template<typename ValueType>
+inline ValueType any_cast(const any& operand)
+{
+    auto p = any_cast<typename std::add_const<typename std::remove_reference<ValueType>::type>::type>(&operand);
+    if(p == nullptr) throw bad_any_cast();
+    return *p;
+}
+
+
+/**
+ * Performs *any_cast<remove_reference_t<ValueType>>(&operand), or throws bad_any_cast on failure.
+ */
+template<typename ValueType>
+inline ValueType any_cast(any& operand)
+{
+    auto p = any_cast<typename std::remove_reference<ValueType>::type>(&operand);
+    if(p == nullptr) throw bad_any_cast();
+    return *p;
+}
+
+
+/**
+ * If ANY_IMPL_ANYCAST_MOVEABLE is not defined, does as N4562 specifies:
+ *     Performs *any_cast<remove_reference_t<ValueType>>(&operand), or throws bad_any_cast on failure.
+ *
+ * If ANY_IMPL_ANYCAST_MOVEABLE is defined, does as LWG Defect 2509 specifies [1]:
+ *     If ValueType is MoveConstructible and isn't a lvalue reference, performs
+ *     std::move(*any_cast<remove_reference_t<ValueType>>(&operand)), otherwise
+ *     *any_cast<remove_reference_t<ValueType>>(&operand).
+ *     Throws bad_any_cast on failure.
+ *
+ *     [1] https://cplusplus.github.io/LWG/lwg-active.html#2509
+ */
+template<typename ValueType>
+inline ValueType any_cast(any&& operand)
+{
+#ifdef ANY_IMPL_ANY_CAST_MOVEABLE
+    using can_move = std::integral_constant<bool, std::is_move_constructible<ValueType>::value && !std::is_lvalue_reference<ValueType>::value>;
+#else
+    using can_move = std::false_type;
+#endif
+
+    auto p = any_cast<typename std::remove_reference<ValueType>::type>(&operand);
+    if(p == nullptr) throw bad_any_cast();
+    return detail::any_cast_move_if_true<ValueType>(p, can_move());
+}
+
+
+/**
+ * If operand != nullptr && operand->type() == typeid(ValueType), a pointer to the object
+ * contained by operand, otherwise nullptr.
+ */
+template<typename T>
+inline const T* any_cast(const any* operand) noexcept
+{
+    if(operand == nullptr || !operand->is_typed(typeid(T)))
+        return nullptr;
+    else
+        return operand->cast<T>();
+}
+
+
+/**
+ * If operand != nullptr && operand->type() == typeid(ValueType), a pointer to the object
+ * contained by operand, otherwise nullptr.
+ */
+template<typename T>
+inline T* any_cast(any* operand) noexcept
+{
+    if(operand == nullptr || !operand->is_typed(typeid(T)))
+        return nullptr;
+    else
+        return operand->cast<T>();
+}
+
+
+inline void swap(any& lhs, any& rhs) noexcept
+{
+    lhs.swap(rhs);
+}
+
+}
+
+#endif /* ANY_H */