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@Quuxplusone @carlcook @nidoizo @Voultapher
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/*
* Boost Software License - Version 1.0 - August 17th, 2003
*
* Permission is hereby granted, free of charge, to any person or organization
* obtaining a copy of the software and accompanying documentation covered by
* this license (the "Software") to use, reproduce, display, distribute,
* execute, and transmit the Software, and to prepare derivative works of the
* Software, and to permit third-parties to whom the Software is furnished to
* do so, all subject to the following:
*
* The copyright notices in the Software and this entire statement, including
* the above license grant, this restriction and the following disclaimer,
* must be included in all copies of the Software, in whole or in part, and
* all derivative works of the Software, unless such copies or derivative
* works are solely in the form of machine-executable object code generated by
* a source language processor.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
* SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
* FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*/
#pragma once
#include <type_traits>
#include <utility>
#include <functional>
#ifndef SG14_INPLACE_FUNCTION_THROW
#define SG14_INPLACE_FUNCTION_THROW(x) throw (x)
#endif
namespace stdext {
namespace inplace_function_detail {
static constexpr size_t InplaceFunctionDefaultCapacity = 32;
#ifndef SG14_USE_STD_ALIGNED_STORAGE
// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61458
// MSVC 32-bit has the same bug.
// libc++ and MSVC 64-bit seem to work fine right now, but why run the risk?
template<size_t Cap>
union aligned_storage_helper {
struct double1 { double a; };
struct double4 { double a[4]; };
template<class T> using maybe = std::conditional_t<(Cap >= sizeof(T)), T, char>;
char real_data[Cap];
maybe<int> a;
maybe<long> b;
maybe<long long> c;
maybe<void*> d;
maybe<void(*)()> e;
maybe<double1> f;
maybe<double4> g;
maybe<long double> h;
};
template<size_t Cap, size_t Align = alignof(aligned_storage_helper<Cap>)>
struct aligned_storage {
using type = std::aligned_storage_t<Cap, Align>;
};
template<size_t Cap, size_t Align = alignof(aligned_storage_helper<Cap>)>
using aligned_storage_t = typename aligned_storage<Cap, Align>::type;
static_assert(sizeof(aligned_storage_t<sizeof(void*)>) == sizeof(void*), "A");
static_assert(alignof(aligned_storage_t<sizeof(void*)>) == alignof(void*), "B");
#else
using std::aligned_storage;
using std::aligned_storage_t;
static_assert(sizeof(std::aligned_storage_t<sizeof(void*)>) == sizeof(void*), "C");
static_assert(alignof(std::aligned_storage_t<sizeof(void*)>) == alignof(void*), "D");
#endif
template<class T> struct wrapper
{
using type = T;
};
template<class R, class... Args> struct vtable
{
using storage_ptr_t = void*;
using invoke_ptr_t = R(*)(storage_ptr_t, Args&&...);
using process_ptr_t = void(*)(storage_ptr_t, storage_ptr_t);
using destructor_ptr_t = void(*)(storage_ptr_t);
const invoke_ptr_t invoke_ptr;
const process_ptr_t copy_ptr;
const process_ptr_t relocate_ptr;
const destructor_ptr_t destructor_ptr;
explicit constexpr vtable() noexcept :
invoke_ptr{ [](storage_ptr_t, Args&&...) -> R
{ SG14_INPLACE_FUNCTION_THROW(std::bad_function_call()); }
},
copy_ptr{ [](storage_ptr_t, storage_ptr_t) -> void {} },
relocate_ptr{ [](storage_ptr_t, storage_ptr_t) -> void {} },
destructor_ptr{ [](storage_ptr_t) -> void {} }
{}
template<class C> explicit constexpr vtable(wrapper<C>) noexcept :
invoke_ptr{ [](storage_ptr_t storage_ptr, Args&&... args) -> R
{ return (*static_cast<C*>(storage_ptr))(
static_cast<Args&&>(args)...
); }
},
copy_ptr{ [](storage_ptr_t dst_ptr, storage_ptr_t src_ptr) -> void
{ ::new (dst_ptr) C{ (*static_cast<C*>(src_ptr)) }; }
},
relocate_ptr{ [](storage_ptr_t dst_ptr, storage_ptr_t src_ptr) -> void
{
::new (dst_ptr) C{ std::move(*static_cast<C*>(src_ptr)) };
static_cast<C*>(src_ptr)->~C();
}
},
destructor_ptr{ [](storage_ptr_t src_ptr) -> void
{ static_cast<C*>(src_ptr)->~C(); }
}
{}
vtable(const vtable&) = delete;
vtable(vtable&&) = delete;
vtable& operator= (const vtable&) = delete;
vtable& operator= (vtable&&) = delete;
~vtable() = default;
};
template<class R, class... Args>
#if __cplusplus >= 201703L
inline constexpr
#endif
vtable<R, Args...> empty_vtable{};
template<size_t DstCap, size_t DstAlign, size_t SrcCap, size_t SrcAlign>
struct is_valid_inplace_dst : std::true_type
{
static_assert(DstCap >= SrcCap,
"Can't squeeze larger inplace_function into a smaller one"
);
static_assert(DstAlign % SrcAlign == 0,
"Incompatible inplace_function alignments"
);
};
// C++11 MSVC compatible implementation of std::is_invocable_r.
template<class R> void accept(R);
template<class, class R, class F, class... Args> struct is_invocable_r_impl : std::false_type {};
template<class F, class... Args> struct is_invocable_r_impl<
decltype(std::declval<F>()(std::declval<Args>()...), void()),
void,
F,
Args...
> : std::true_type {};
template<class F, class... Args> struct is_invocable_r_impl<
decltype(std::declval<F>()(std::declval<Args>()...), void()),
const void,
F,
Args...
> : std::true_type {};
template<class R, class F, class... Args> struct is_invocable_r_impl<
decltype(accept<R>(std::declval<F>()(std::declval<Args>()...))),
R,
F,
Args...
> : std::true_type {};
template<class R, class F, class... Args> using is_invocable_r = is_invocable_r_impl<
void,
R,
F,
Args...
>;
} // namespace inplace_function_detail
template<
class Signature,
size_t Capacity = inplace_function_detail::InplaceFunctionDefaultCapacity,
size_t Alignment = alignof(inplace_function_detail::aligned_storage_t<Capacity>)
>
class inplace_function; // unspecified
namespace inplace_function_detail {
template<class> struct is_inplace_function : std::false_type {};
template<class Sig, size_t Cap, size_t Align>
struct is_inplace_function<inplace_function<Sig, Cap, Align>> : std::true_type {};
} // namespace inplace_function_detail
template<
class R,
class... Args,
size_t Capacity,
size_t Alignment
>
class inplace_function<R(Args...), Capacity, Alignment>
{
using storage_t = inplace_function_detail::aligned_storage_t<Capacity, Alignment>;
using vtable_t = inplace_function_detail::vtable<R, Args...>;
using vtable_ptr_t = const vtable_t*;
template <class, size_t, size_t> friend class inplace_function;
public:
using capacity = std::integral_constant<size_t, Capacity>;
using alignment = std::integral_constant<size_t, Alignment>;
inplace_function() noexcept :
vtable_ptr_{std::addressof(inplace_function_detail::empty_vtable<R, Args...>)}
{}
template<
class T,
class C = std::decay_t<T>,
class = std::enable_if_t<
!inplace_function_detail::is_inplace_function<C>::value
&& inplace_function_detail::is_invocable_r<R, C&, Args...>::value
>
>
inplace_function(T&& closure)
{
static_assert(std::is_copy_constructible<C>::value,
"inplace_function cannot be constructed from non-copyable type"
);
static_assert(sizeof(C) <= Capacity,
"inplace_function cannot be constructed from object with this (large) size"
);
static_assert(Alignment % alignof(C) == 0,
"inplace_function cannot be constructed from object with this (large) alignment"
);
static const vtable_t vt{inplace_function_detail::wrapper<C>{}};
vtable_ptr_ = std::addressof(vt);
::new (std::addressof(storage_)) C{std::forward<T>(closure)};
}
template<size_t Cap, size_t Align>
inplace_function(const inplace_function<R(Args...), Cap, Align>& other)
: inplace_function(other.vtable_ptr_, other.vtable_ptr_->copy_ptr, std::addressof(other.storage_))
{
static_assert(inplace_function_detail::is_valid_inplace_dst<
Capacity, Alignment, Cap, Align
>::value, "conversion not allowed");
}
template<size_t Cap, size_t Align>
inplace_function(inplace_function<R(Args...), Cap, Align>&& other) noexcept
: inplace_function(other.vtable_ptr_, other.vtable_ptr_->relocate_ptr, std::addressof(other.storage_))
{
static_assert(inplace_function_detail::is_valid_inplace_dst<
Capacity, Alignment, Cap, Align
>::value, "conversion not allowed");
other.vtable_ptr_ = std::addressof(inplace_function_detail::empty_vtable<R, Args...>);
}
inplace_function(std::nullptr_t) noexcept :
vtable_ptr_{std::addressof(inplace_function_detail::empty_vtable<R, Args...>)}
{}
inplace_function(const inplace_function& other) :
vtable_ptr_{other.vtable_ptr_}
{
vtable_ptr_->copy_ptr(
std::addressof(storage_),
std::addressof(other.storage_)
);
}
inplace_function(inplace_function&& other) noexcept :
vtable_ptr_{std::exchange(other.vtable_ptr_, std::addressof(inplace_function_detail::empty_vtable<R, Args...>))}
{
vtable_ptr_->relocate_ptr(
std::addressof(storage_),
std::addressof(other.storage_)
);
}
inplace_function& operator= (std::nullptr_t) noexcept
{
vtable_ptr_->destructor_ptr(std::addressof(storage_));
vtable_ptr_ = std::addressof(inplace_function_detail::empty_vtable<R, Args...>);
return *this;
}
inplace_function& operator= (inplace_function other) noexcept
{
vtable_ptr_->destructor_ptr(std::addressof(storage_));
vtable_ptr_ = std::exchange(other.vtable_ptr_, std::addressof(inplace_function_detail::empty_vtable<R, Args...>));
vtable_ptr_->relocate_ptr(
std::addressof(storage_),
std::addressof(other.storage_)
);
return *this;
}
~inplace_function()
{
vtable_ptr_->destructor_ptr(std::addressof(storage_));
}
R operator() (Args... args) const
{
return vtable_ptr_->invoke_ptr(
std::addressof(storage_),
std::forward<Args>(args)...
);
}
constexpr bool operator== (std::nullptr_t) const noexcept
{
return !operator bool();
}
constexpr bool operator!= (std::nullptr_t) const noexcept
{
return operator bool();
}
explicit constexpr operator bool() const noexcept
{
return vtable_ptr_ != std::addressof(inplace_function_detail::empty_vtable<R, Args...>);
}
void swap(inplace_function& other) noexcept
{
if (this == std::addressof(other)) return;
storage_t tmp;
vtable_ptr_->relocate_ptr(
std::addressof(tmp),
std::addressof(storage_)
);
other.vtable_ptr_->relocate_ptr(
std::addressof(storage_),
std::addressof(other.storage_)
);
vtable_ptr_->relocate_ptr(
std::addressof(other.storage_),
std::addressof(tmp)
);
std::swap(vtable_ptr_, other.vtable_ptr_);
}
friend void swap(inplace_function& lhs, inplace_function& rhs) noexcept
{
lhs.swap(rhs);
}
private:
vtable_ptr_t vtable_ptr_;
mutable storage_t storage_;
inplace_function(
vtable_ptr_t vtable_ptr,
typename vtable_t::process_ptr_t process_ptr,
typename vtable_t::storage_ptr_t storage_ptr
) : vtable_ptr_{vtable_ptr}
{
process_ptr(std::addressof(storage_), storage_ptr);
}
};
} // namespace stdext
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