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util::function bugfixes & strong exception guarantee

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This commit is contained in:
Nikita Lisitsa 2020-11-23 17:56:35 +03:00
parent cb468aa675
commit c6fe38989c
1 changed files with 60 additions and 17 deletions
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77
libs/util/include/psemek/util/function.hpp
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@ -20,6 +20,22 @@ namespace psemek::util
template <typename R, typename ... Args>
struct function<R(Args...)>
{
private:
static constexpr std::size_t storage_size = sizeof(void*) * 3;
static constexpr std::size_t storage_align = alignof(void*);
template <typename T>
struct uses_static_storage
: std::bool_constant<true
&& sizeof(T) <= storage_size
&& alignof(T) <= storage_align
&& ((storage_align % alignof(T)) == 0)
&& std::is_nothrow_move_constructible_v<T>
>
{};
public:
using signature = R(Args...);
function() noexcept = default;
@ -33,8 +49,18 @@ namespace psemek::util
function (function const &) = delete;
function & operator = (function const &) = delete;
~function();
// operator = (F && f) has strong exception guarantree:
// if the assignment throws, the function remains unchanged
template <typename F>
function & operator = (F && f);
std::enable_if_t<uses_static_storage<std::decay_t<F>>::value, function &>
operator = (F && f);
template <typename F>
std::enable_if_t<!uses_static_storage<std::decay_t<F>>::value, function &>
operator = (F && f);
explicit operator bool() const
{
@ -46,10 +72,9 @@ namespace psemek::util
void reset();
private:
static constexpr std::size_t storage_size = sizeof(void*) * 3;
static constexpr std::size_t storage_align = alignof(void*);
void swap(function & other) noexcept;
private:
std::aligned_storage_t<storage_size, storage_align> storage_;
struct vtable
@ -78,18 +103,29 @@ namespace psemek::util
template <typename R, typename ... Args>
template <typename F>
function<R(Args...)> & function<R(Args...)>::operator = (F && f)
std::enable_if_t<function<R(Args...)>::template uses_static_storage<std::decay_t<F>>::value, function<R(Args...)> &>
function<R(Args...)>::operator = (F && f)
{
reset();
assign(std::forward<F>(f));
return *this;
}
template <typename R, typename ... Args>
template <typename F>
std::enable_if_t<!function<R(Args...)>::template uses_static_storage<std::decay_t<F>>::value, function<R(Args...)> &>
function<R(Args...)>::operator = (F && f)
{
function(std::forward<F>(f)).swap(*this);
return *this;
}
template <typename R, typename ... Args>
function<R(Args...)>::function (function && other) noexcept
{
vtable_ = other.vtable_;
vtable_->move(&other.storage_, &storage_);
if (vtable_)
vtable_->move(&other.storage_, &storage_);
other.reset();
}
@ -99,12 +135,20 @@ namespace psemek::util
if (this == &other)
return *this;
reset();
vtable_ = other.vtable_;
vtable_->move(&other.storage_, &storage_);
if (vtable_)
vtable_->move(&other.storage_, &storage_);
other.reset();
return *this;
}
template <typename R, typename ... Args>
function<R(Args...)>::~function()
{
reset();
}
template <typename R, typename ... Args>
template <typename ... Args1>
R function<R(Args...)>::operator()(Args1 && ... args) const
@ -124,27 +168,26 @@ namespace psemek::util
vtable_ = nullptr;
}
template <typename R, typename ... Args>
void function<R(Args...)>::swap(function & other) noexcept
{
std::swap(*this, other);
}
template <typename R, typename ... Args>
template <typename F>
void function<R(Args...)>::assign(F && f)
{
using T = std::decay_t<F>;
constexpr bool static_storage = true
&& sizeof(T) <= storage_size
&& alignof(T) <= storage_align
&& ((storage_align % alignof(T)) == 0)
&& std::is_nothrow_move_constructible_v<T>
;
if constexpr (static_storage)
if constexpr (uses_static_storage<T>::value)
{
new (reinterpret_cast<T *>(&storage_)) T(std::move(f));
static vtable m = {
[](void * src, void * dst){ new (reinterpret_cast<T*>(dst)) T(std::move(*reinterpret_cast<T*>(src))); },
[](void * src){ reinterpret_cast<T*>(src)->~T(); },
[](void * src, Args ... args) -> R { return (*reinterpret_cast<T*>(src))(static_cast<Args&&>(args)...); }
[](void * src, Args ... args) -> R { return std::invoke(*reinterpret_cast<T*>(src), static_cast<Args&&>(args)...); }
};
vtable_ = &m;
@ -156,7 +199,7 @@ namespace psemek::util
static vtable m = {
[](void * src, void * dst){ *reinterpret_cast<T**>(dst) = *reinterpret_cast<T**>(src); *reinterpret_cast<T**>(src) = nullptr; },
[](void * src){ delete *reinterpret_cast<T**>(src); },
[](void * src, Args ... args) -> R { return (**reinterpret_cast<T**>(src))(static_cast<Args&&>(args)...); }
[](void * src, Args ... args) -> R { return std::invoke(**reinterpret_cast<T**>(src), static_cast<Args&&>(args)...); }
};
vtable_ = &m;