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Fix UB of potentially wrong compile-time assumption of transparently replaceable #81

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merged 1 commit into from
Apr 6, 2024
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Fix UB of potentially wrong compile-time assumption of transparently replaceable #81

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28 changes: 13 additions & 15 deletions proxy.h
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Original file line number Diff line number Diff line change
Expand Up @@ -165,13 +165,12 @@ R invoke_dispatch(Args&&... args) {
}
}
template <class F, bool NE, class R, class... Args>
R dispatcher_default_impl(const char*, Args... args) noexcept(NE) {
return invoke_dispatch<F, R>(std::forward<Args>(args)...);
}
R dispatcher_default_impl(const char*, Args... args) noexcept(NE)
{ return invoke_dispatch<F, R>(std::forward<Args>(args)...); }
template <class P, class F, bool NE, class R, class... Args>
R dispatcher_impl(const char* erased, Args... args) noexcept(NE) {
return invoke_dispatch<F, R>(ptr_traits<P>::dereference(
*reinterpret_cast<const P*>(erased)), std::forward<Args>(args)...);
return invoke_dispatch<F, R>(ptr_traits<P>::dereference(*std::launder(
reinterpret_cast<const P*>(erased))), std::forward<Args>(args)...);
}
template <bool NE, class R, class... Args>
struct overload_traits_impl : applicable_traits {
Expand Down Expand Up @@ -274,7 +273,7 @@ struct copyability_meta_provider {
static constexpr func_ptr_t<NE, void, char*, const char*> get() {
return [](char* self, const char* rhs) noexcept(NE) {
std::construct_at(reinterpret_cast<P*>(self),
*reinterpret_cast<const P*>(rhs));
*std::launder(reinterpret_cast<const P*>(rhs)));
};
}
};
Expand All @@ -283,9 +282,9 @@ struct relocatability_meta_provider {
template <class P>
static constexpr func_ptr_t<NE, void, char*, char*> get() {
return [](char* self, char* rhs) noexcept(NE) {
std::construct_at(reinterpret_cast<P*>(self),
std::move(*reinterpret_cast<P*>(rhs)));
std::destroy_at(reinterpret_cast<P*>(rhs));
P* other = std::launder(reinterpret_cast<P*>(rhs));
std::construct_at(reinterpret_cast<P*>(self), std::move(*other));
std::destroy_at(other);
};
}
};
Expand All @@ -294,7 +293,7 @@ struct destructibility_meta_provider {
template <class P>
static constexpr func_ptr_t<NE, void, char*> get() {
return [](char* self) noexcept(NE)
{ std::destroy_at(reinterpret_cast<P*>(self)); };
{ std::destroy_at(std::launder(reinterpret_cast<P*>(self))); };
}
};
template <template <bool> class MP, constraint_level C>
Expand Down Expand Up @@ -591,16 +590,14 @@ class proxy {
P& emplace(Args&&... args) noexcept(HasNothrowPolyAssignment<P, Args...>)
requires(HasPolyAssignment<P, Args...>) {
reset();
initialize<P>(std::forward<Args>(args)...);
return *reinterpret_cast<P*>(ptr_);
return initialize<P>(std::forward<Args>(args)...);
}
template <class P, class U, class... Args>
P& emplace(std::initializer_list<U> il, Args&&... args)
noexcept(HasNothrowPolyAssignment<P, std::initializer_list<U>&, Args...>)
requires(HasPolyAssignment<P, std::initializer_list<U>&, Args...>) {
reset();
initialize<P>(il, std::forward<Args>(args)...);
return *reinterpret_cast<P*>(ptr_);
return initialize<P>(il, std::forward<Args>(args)...);
}
template <class D = DefaultDispatch, class... Args>
decltype(auto) invoke(Args&&... args) const
Expand All @@ -619,9 +616,10 @@ class proxy {

private:
template <class P, class... Args>
void initialize(Args&&... args) {
P& initialize(Args&&... args) {
std::construct_at(reinterpret_cast<P*>(ptr_), std::forward<Args>(args)...);
meta_ = details::meta_ptr<typename Traits::meta>{std::in_place_type<P>};
return *std::launder(reinterpret_cast<P*>(ptr_));
}

details::meta_ptr<typename Traits::meta> meta_;
Expand Down
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