Any.hpp

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/* 
 * Any.hpp 
 *
 * This file is part of the Chemical Data Processing Toolkit
 *
 * Copyright (C) 2003 Thomas Seidel <thomas.seidel@univie.ac.at>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library; see the file COPYING. If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */
 
#ifndef CDPL_BASE_ANY_HPP
#define CDPL_BASE_ANY_HPP
 
#include <string>
#include <typeinfo>
#include <type_traits>
#include <stdexcept>
#include <utility>
#include <new>
 
#include "CDPL/Base/Exceptions.hpp"
 
 
namespace CDPL
{
 
    namespace Base
    {
 
        class Any final
        {
 
          public:
            Any() noexcept : vtable(nullptr) {}
 
            Any(const Any& rhs):
                vtable(rhs.vtable)
            {
                if (!rhs.isEmpty())
                    rhs.vtable->copy(rhs.storage, this->storage);
            }
 
            Any(Any&& rhs) noexcept : vtable(rhs.vtable)
            {
                if (!rhs.isEmpty()) {
                    rhs.vtable->move(rhs.storage, this->storage);
                    rhs.vtable = nullptr;
                }
            }
 
            ~Any()
            {
                this->clear();
            }
 
            template <typename ValueType, typename = typename std::enable_if<!std::is_same<typename std::decay<ValueType>::type, Any>::value>::type>
            Any(ValueType&& val)
            {
                static_assert(std::is_copy_constructible<typename std::decay<ValueType>::type>::value,
                              "ValueType shall satisfy CopyConstructible requirements.");
 
                this->construct(std::forward<ValueType>(val));
            }
 
            Any& operator=(const Any& rhs)
            {
                Any(rhs).swap(*this);
                return *this;
            }
 
            Any& operator=(Any&& rhs) noexcept
            {
                Any(std::move(rhs)).swap(*this);
                return *this;
            }
 
            template <typename ValueType, typename = typename std::enable_if<!std::is_same<typename std::decay<ValueType>::type, Any>::value>::type>
            Any& operator=(ValueType&& val)
            {
                static_assert(std::is_copy_constructible<typename std::decay<ValueType>::type>::value,
                              "T shall satisfy CopyConstructible requirements.");
 
                Any(std::forward<ValueType>(val)).swap(*this);
                return *this;
            }
 
            void clear() noexcept
            {
                if (!isEmpty()) {
                    this->vtable->destroy(storage);
                    this->vtable = nullptr;
                }
            }
 
            bool isEmpty() const noexcept
            {
                return (this->vtable == nullptr);
            }
 
            const std::type_info& getTypeID() const noexcept
            {
                return (isEmpty() ? typeid(void) : this->vtable->type());
            }
 
            void swap(Any& rhs) noexcept
            {
                if (this->vtable != rhs.vtable) {
                    Any tmp(std::move(rhs));
 
                    // move from *this to rhs.
                    rhs.vtable = this->vtable;
 
                    if (this->vtable != nullptr) {
                        this->vtable->move(this->storage, rhs.storage);
                        //this->vtable = nullptr; -- unneeded, see below
                    }
 
                    // move from tmp (previously rhs) to *this.
                    this->vtable = tmp.vtable;
 
                    if (tmp.vtable != nullptr) {
                        tmp.vtable->move(tmp.storage, this->storage);
                        tmp.vtable = nullptr;
                    }
 
                } else { // same types
                    if (this->vtable != nullptr)
                        this->vtable->swap(this->storage, rhs.storage);
                }
            }
 
            template <typename ValueType>
            const ValueType& getData() const
            {
                if (this->isEmpty())
                    throw BadCast("Any: empty");
 
                using T = typename std::decay<ValueType>::type;
 
                if (this->isTyped(typeid(T)))
                    return *this->cast<T>();
 
                throw BadCast(std::string("Any: extraction of stored value of type '") + this->getTypeID().name() +
                              std::string("' as type '") + typeid(T).name() + "' not possible");
            }
 
            const void* getDataPointer() const noexcept
            {
                if (isEmpty())
                    return nullptr;
 
                return this->vtable->data(this->storage);
            }
 
          private:
            // Storage and Virtual Method Table
            union Storage
            {
                using StackStorageT = typename std::aligned_storage<2 * sizeof(void*), std::alignment_of<void*>::value>::type;
 
                void*         dynamic;
                StackStorageT stack; // 2 words for e.g. shared_ptr
            };
 
            // Base VTable specification.
            struct VTable
            {
                // Note: The caller is responssible for doing .vtable = nullptr after destructful operations
                // such as destroy() and/or move().
 
                // 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&) 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& src, Storage& 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& src, Storage& dest) noexcept;
 
                // Exchanges the storage between lhs and rhs.
                void (*swap)(Storage& lhs, Storage& rhs) noexcept;
 
                const void* (*data)(const Storage& storage)noexcept;
            };
 
            // VTable for dynamically allocated storage.
            template <typename T>
            struct VTableDynamic
            {
 
                static const std::type_info& type() noexcept
                {
                    return typeid(T);
                }
 
                static void destroy(Storage& storage) noexcept
                {
                    //assert(reinterpret_cast<T*>(storage.dynamic));
                    delete reinterpret_cast<T*>(storage.dynamic);
                }
 
                static void copy(const Storage& src, Storage& dest)
                {
                    dest.dynamic = new T(*reinterpret_cast<const T*>(src.dynamic));
                }
 
                static void move(Storage& src, Storage& dest) noexcept
                {
                    dest.dynamic = src.dynamic;
                    src.dynamic  = nullptr;
                }
 
                static void swap(Storage& lhs, Storage& rhs) noexcept
                {
                    // just exchage the storage pointers.
                    std::swap(lhs.dynamic, rhs.dynamic);
                }
 
                static const void* data(const Storage& storage) noexcept
                {
                    return storage.dynamic;
                }
            };
 
            // VTable for stack allocated storage.
            template <typename T>
            struct VTableStack
            {
 
                static const std::type_info& type() noexcept
                {
                    return typeid(T);
                }
 
                static void destroy(Storage& storage) noexcept
                {
                    reinterpret_cast<T*>(&storage.stack)->~T();
                }
 
                static void copy(const Storage& src, Storage& dest)
                {
                    new (&dest.stack) T(reinterpret_cast<const T&>(src.stack));
                }
 
                static void move(Storage& src, Storage& dest) noexcept
                {
                    // one of the conditions for using VTableStack 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& lhs, Storage& rhs) noexcept
                {
                    Storage tmp_storage;
 
                    move(rhs, tmp_storage);
                    move(lhs, rhs);
                    move(tmp_storage, lhs);
                }
 
                static const void* data(const Storage& storage) noexcept
                {
                    return &storage.stack;
                }
            };
 
            // Whether the type T must be dynamically allocated or can be stored on the stack.
            template <typename T>
            struct RequiresAlloc : std::integral_constant<bool,
                                                          !(std::is_nothrow_move_constructible<T>::value // N4562 §6.3/3 [any.class]
                                                            && sizeof(T) <= sizeof(Storage::stack) && std::alignment_of<T>::value <= std::alignment_of<Storage::StackStorageT>::value)>
            {};
 
            // Returns the pointer to the vtable of the type T.
            template <typename T>
            static VTable* getVTableForType()
            {
 
                using VTableType = typename std::conditional<RequiresAlloc<T>::value, VTableDynamic<T>, VTableStack<T> >::type;
 
                static VTable table = {
                    VTableType::type,
                    VTableType::destroy,
                    VTableType::copy,
                    VTableType::move,
                    VTableType::swap,
                    VTableType::data,
                };
 
                return &table;
            }
 
            // Same effect as is_same(this->getTypeID(), t);
            bool isTyped(const std::type_info& t) const
            {
                return (this->getTypeID() == t);
            }
 
            // Casts (with no type_info checks) the storage pointer as const T*.
            template <typename T>
            const T* cast() const noexcept
            {
                return RequiresAlloc<T>::value ? reinterpret_cast<const T*>(storage.dynamic) :
                                                 reinterpret_cast<const T*>(&storage.stack);
            }
 
            template <typename ValueType, typename T>
            typename std::enable_if<RequiresAlloc<T>::value>::type
            doConstruct(ValueType&& value)
            {
                storage.dynamic = new T(std::forward<ValueType>(value));
            }
 
            template <typename ValueType, typename T>
            typename std::enable_if<!RequiresAlloc<T>::value>::type
            doConstruct(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 = getVTableForType<T>();
 
                doConstruct<ValueType, T>(std::forward<ValueType>(value));
            }
 
            Storage storage; // on offset(0) so no padding for align
            VTable* vtable;
        };
 
        template <>
        inline const Any& Any::getData<Any>() const
        {
            return *this;
        }
    } // namespace Base
} // namespace CDPL
 
 
// \cond DOC_IMPL_DETAILS
 
namespace std
{
 
    inline void swap(CDPL::Base::Any& lhs, CDPL::Base::Any& rhs) noexcept
    {
        lhs.swap(rhs);
    }
} // namespace std
 
// \endcond
 
#endif // CDPL_BASE_ANY_HPP