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Михаил Капелько 6 months ago
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/**
* 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 Merc?s 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) {
std::cout << "libany err-01\n";

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 */

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