/*
* Copyright (c) Meta Platforms, Inc. and affiliates.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#pragma once
#include <functional>
#include <new>
#include <tuple>
#include <type_traits>
#include <typeinfo>
#include <utility>
#include <folly/PolyException.h>
#include <folly/Portability.h>
#include <folly/Traits.h>
#include <folly/Utility.h>
#include <folly/detail/TypeList.h>
#include <folly/functional/Invoke.h>
#include <folly/lang/Exception.h>
#include <folly/lang/StaticConst.h>
namespace folly {
/// \cond
namespace detail {
template <class I>
struct PolyRoot;
using RRef_ = MetaQuoteTrait<std::add_rvalue_reference>;
using LRef_ = MetaQuoteTrait<std::add_lvalue_reference>;
template <typename T>
struct XRef_ : Type<MetaQuoteTrait<Type>> {};
template <typename T>
using XRef = _t<XRef_<T>>;
template <typename T>
struct XRef_<T&&> : Type<MetaCompose<RRef_, XRef<T>>> {};
template <typename T>
struct XRef_<T&> : Type<MetaCompose<LRef_, XRef<T>>> {};
template <typename T>
struct XRef_<T const> : Type<MetaQuoteTrait<std::add_const>> {};
template <class A, class B>
using AddCvrefOf = MetaApply<XRef<B>, A>;
} // namespace detail
/// \endcond
template <class I>
struct Poly;
template <class T, class I>
detail::AddCvrefOf<T, I>& poly_cast(detail::PolyRoot<I>&);
template <class T, class I>
detail::AddCvrefOf<T, I> const& poly_cast(detail::PolyRoot<I> const&);
template <auto...>
struct PolyMembers;
/// \cond
namespace detail {
/* *****************************************************************************
* IMPLEMENTATION NOTES
*
Building the Interface
----------------------
Here is a high-level description of how Poly works. Users write an interface
such as:
struct Mine {
template <class Base>
struct Interface {
int Exec() const {
return folly::poly_call<0>(*this);
}
}
template <class T>
using Members = folly::PolyMembers<&T::Exec>;
};
Then they instantiate Poly<Mine>, which will have an Exec member function
of the correct signature. The Exec member function comes from
Mine::Interface<PolyNode<Mine, PolyRoot<Mine>>>, from which Poly<Mine> inherits.
Here's what each piece means:
- PolyRoot<I>: stores Data, which is a union of a void* (used when the Poly is
storing an object on the heap or a reference) and some aligned storage (used
when the Poly is storing an object in-situ). PolyRoot also stores a vtable
pointer for interface I, which is a pointer to a struct containing function
pointers. The function pointers are bound member functions (e.g.,
SomeType::Exec). More on the vtable pointer and how it is generated below.
- PolyNode: provides the hooks used by folly::poly_call to dispatch to the
correctly bound member function for this interface. In the context of an
interface I, folly::poly_call<K>(*this, args...) will:
1. Fetch the vtable pointer from PolyRoot,
2. Select the I portion of that vtable (which, in the case of interface
extension, may only be a part of the total vtable),
3. Fetch the K-th function pointer from that vtable part,
4. Call through that function pointer, passing Data (from PolyRoot) and any
additional arguments in the folly::poly_call<K> invocation.
In the case of interface extension -- for instance, if interface Mine extended
interface Yours by inheriting from PolyExtends<Yours> -- then interface Mine
will have a list of base interfaces in a typelist called "Subsumptions".
Poly<Mine> will fold all the subsumed interfaces together, linearly inheriting
from them. To take the example of an interface Mine that extends Yours,
Poly<Mine> would inherit from this type:
Mine::Interface<
PolyNode<Mine,
Your::Interface<
PolyNode<Your, PolyRoot<Mine>>>>>
Through linear inheritance, Poly<Mine> ends up with the public member functions
of both interfaces, Mine and Yours.
VTables
-------
As mentioned above, PolyRoot<I> stores a vtable pointer for interface I. The
vtable is a struct whose members are function pointers. How are the types of
those function pointers computed from the interface? A dummy type is created,
Archetype<I>, in much the same way that Poly<I>'s base type is computed. Instead
of PolyNode and PolyRoot, there is ArchetypeNode and ArchetypeRoot. These types
also provide hooks for folly::poly_call, but they are dummy hooks that do
nothing. (Actually, they call std::terminate; they will never be called.) Once
Archetype<I> has been constructed, it is a concrete type that has all the
member functions of the interface and its subsumed interfaces. That type is
passed to Mine::Members, which takes the address of Archetype<I>::Exec and
inspects the resulting member function type. This is done for each member in the
interface. From a list of [member] function pointers, it is a simple matter of
metaprogramming to build a struct of function pointers. std::tuple is used for
this.
An extra field is added to the tuple for a function that handles all of the
"special" operations: destruction, copying, moving, getting the type
information, getting the address of the stored object, and fetching a fixed-up
vtable pointer for reference conversions (e.g., I -> I&, I& -> I const&, etc).
Subsumed interfaces are handled by having VTable<IDerived> inherit from
BasePtr<IBase>, where BasePtr<IBase> has only one member of type
VTable<IBase> const*.
Now that the type of VTable<I> is computed, how are the fields populated?
Poly<I> default-constructs to an empty state. Its vtable pointer points to a
vtable whose fields are initialized with the addresses of functions that do
nothing but throw a BadPolyAccess exception. That way, if you call a member
function on an empty Poly, you get an exception. The function pointer
corresponding to the "special" operations points to a no-op function; copying,
moving and destroying an empty Poly does nothing.
On the other hand, when you pass an object of type T satisfying interface I to
Poly<I>'s constructor or assignment operator, a vtable for {I,T} is reified by
passing type T to I::Members, thereby creating a list of bindings for T's member
functions. The address of this vtable gets stored in the PolyRoot<I> subobject,
imbuing the Poly object with the behaviors of type T. The T object itself gets
stored either on the heap or in the aligned storage within the Poly object
itself, depending on the size of T and whether or not it has a noexcept move
constructor.
*/
template <class T, template <class...> class U>
struct IsInstanceOf : std::false_type {};
template <class... Ts, template <class...> class U>
struct IsInstanceOf<U<Ts...>, U> : std::true_type {};
template <class Then>
decltype(auto) if_constexpr(std::true_type, Then then) {
return then(Identity{});
}
template <class Then>
void if_constexpr(std::false_type, Then) {}
template <class Then, class Else>
decltype(auto) if_constexpr(std::true_type, Then then, Else) {
return then(Identity{});
}
template <class Then, class Else>
decltype(auto) if_constexpr(std::false_type, Then, Else else_) {
return else_(Identity{});
}
enum class Op : short { eNuke, eMove, eCopy, eType, eAddr, eRefr };
enum class RefType : std::uintptr_t { eRvalue, eLvalue, eConstLvalue };
struct Data;
template <class I>
struct PolyVal;
template <class I>
struct PolyRef;
struct PolyAccess;
template <class T>
using IsPoly = IsInstanceOf<remove_cvref_t<T>, Poly>;
// Given an interface I and a concrete type T that satisfies the interface
// I, create a list of member function bindings from members of T to members
// of I.
template <class I, class T>
using MembersOf = typename I::template Members<remove_cvref_t<T>>;
// Given an interface I and a base type T, create a type that implements
// the interface I in terms of the capabilities of T.
template <class I, class T>
using InterfaceOf = typename I::template Interface<T>;
struct PolyBase {};
template <class I, class = void>
struct SubsumptionsOf_ {
using type = TypeList<>;
};
template <class I>
using InclusiveSubsumptionsOf = TypePushFront<_t<SubsumptionsOf_<I>>, I>;
template <class I>
struct SubsumptionsOf_<I, void_t<typename I::Subsumptions>> {
using type = TypeJoin<TypeTransform<
typename I::Subsumptions,
MetaQuote<InclusiveSubsumptionsOf>>>;
};
template <class I>
using SubsumptionsOf = TypeReverseUnique<_t<SubsumptionsOf_<I>>>;
struct Bottom {
template <class T>
[[noreturn]] /* implicit */ operator T&&() const {
std::terminate();
}
};
using ArchetypeNode = MetaQuote<InterfaceOf>;
template <class I>
struct ArchetypeRoot;
template <class I>
using Archetype =
TypeFold<InclusiveSubsumptionsOf<I>, ArchetypeRoot<I>, ArchetypeNode>;
struct ArchetypeBase : Bottom {
ArchetypeBase() = default;
template <class T>
/* implicit */ ArchetypeBase(T&&);
template <std::size_t, class... As>
[[noreturn]] Bottom _polyCall_(As&&...) const {
std::terminate();
}
friend bool operator==(ArchetypeBase const&, ArchetypeBase const&);
friend bool operator!=(ArchetypeBase const&, ArchetypeBase const&);
friend bool operator<(ArchetypeBase const&, ArchetypeBase const&);
friend bool operator<=(ArchetypeBase const&, ArchetypeBase const&);
friend bool operator>(ArchetypeBase const&, ArchetypeBase const&);
friend bool operator>=(ArchetypeBase const&, ArchetypeBase const&);
friend Bottom operator++(ArchetypeBase const&);
friend Bottom operator++(ArchetypeBase const&, int);
friend Bottom operator--(ArchetypeBase const&);
friend Bottom operator--(ArchetypeBase const&, int);
friend Bottom operator+(ArchetypeBase const&, ArchetypeBase const&);
friend Bottom operator+=(ArchetypeBase const&, ArchetypeBase const&);
friend Bottom operator-(ArchetypeBase const&, ArchetypeBase const&);
friend Bottom operator-=(ArchetypeBase const&, ArchetypeBase const&);
friend Bottom operator*(ArchetypeBase const&, ArchetypeBase const&);
friend Bottom operator*=(ArchetypeBase const&, ArchetypeBase const&);
friend Bottom operator/(ArchetypeBase const&, ArchetypeBase const&);
friend Bottom operator/=(ArchetypeBase const&, ArchetypeBase const&);
friend Bottom operator%(ArchetypeBase const&, ArchetypeBase const&);
friend Bottom operator%=(ArchetypeBase const&, ArchetypeBase const&);
friend Bottom operator<<(ArchetypeBase const&, ArchetypeBase const&);
friend Bottom operator<<=(ArchetypeBase const&, ArchetypeBase const&);
friend Bottom operator>>(ArchetypeBase const&, ArchetypeBase const&);
friend Bottom operator>>=(ArchetypeBase const&, ArchetypeBase const&);
};
template <class I>
struct ArchetypeRoot : ArchetypeBase {
template <class Node, class Tfx>
using _polySelf_ = Archetype<AddCvrefOf<MetaApply<Tfx, I>, Node>>;
using _polyInterface_ = I;
};
struct Data {
Data() = default;
// Suppress compiler-generated copy ops to not copy anything:
Data(Data const&) {}
Data& operator=(Data const&) { return *this; }
union {
void* pobj_ = nullptr;
std::aligned_storage_t<sizeof(double[2])> buff_;
};
};
template <class U, class I>
using Arg =
If<std::is_same<remove_cvref_t<U>, Archetype<I>>::value,
Poly<AddCvrefOf<I, U const&>>,
U>;
template <class U, class I>
using Ret =
If<std::is_same<remove_cvref_t<U>, Archetype<I>>::value,
AddCvrefOf<Poly<I>, U>,
U>;
template <class Member, class I>
struct SignatureOf_;
template <class R, class C, class... As, class I>
struct SignatureOf_<R (C::*)(As...), I> {
using type = Ret<R, I> (*)(Data&, Arg<As, I>...);
};
template <class R, class C, class... As, class I>
struct SignatureOf_<R (C::*)(As...) const, I> {
using type = Ret<R, I> (*)(Data const&, Arg<As, I>...);
};
template <class R, class C, class... As, class I>
struct SignatureOf_<R (C::*)(As...) noexcept, I> {
using type = std::add_pointer_t<Ret<R, I>(Data&, Arg<As, I>...) noexcept>;
};
template <class R, class C, class... As, class I>
struct SignatureOf_<R (C::*)(As...) const noexcept, I> {
using type =
std::add_pointer_t<Ret<R, I>(Data const&, Arg<As, I>...) noexcept>;
};
template <class R, class This, class... As, class I>
struct SignatureOf_<R (*)(This&, As...), I> {
using type = Ret<R, I> (*)(Data&, Arg<As, I>...);
};
template <class R, class This, class... As, class I>
struct SignatureOf_<R (*)(This const&, As...), I> {
using type = Ret<R, I> (*)(Data const&, Arg<As, I>...);
};
template <auto Arch, class I>
using SignatureOf = _t<SignatureOf_<decltype(Arch), I>>;
template <auto User, class I, class Sig = SignatureOf<User, I>>
struct ArgTypes_;
template <auto User, class I, class Ret, class Data, class... Args>
struct ArgTypes_<User, I, Ret (*)(Data, Args...)> {
using type = TypeList<Args...>;
};
template <auto User, class I, class Ret, class Data, class... Args>
struct ArgTypes_<User, I, Ret (*)(Data, Args...) noexcept> {
using type = TypeList<Args...>;
};
template <auto User, class I>
using ArgTypes = _t<ArgTypes_<User, I>>;
template <class R, class... Args>
using FnPtr = R (*)(Args...);
struct ThrowThunk {
template <class R, class... Args>
constexpr /* implicit */ operator FnPtr<R, Args...>() const noexcept {
struct _ {
static R call(Args...) { throw_exception<BadPolyAccess>(); }
};
return &_::call;
}
};
inline constexpr ThrowThunk throw_() noexcept {
return ThrowThunk{};
}
template <class T>
inline constexpr bool inSitu() noexcept {
return !std::is_reference<T>::value &&
sizeof(std::decay_t<T>) <= sizeof(Data) &&
std::is_nothrow_move_constructible<std::decay_t<T>>::value;
}
template <class T>
T& get(Data& d) noexcept {
if (inSitu<T>()) {
return *(std::add_pointer_t<T>)static_cast<void*>(&d.buff_);
} else {
return *static_cast<std::add_pointer_t<T>>(d.pobj_);
}
}
template <class T>
T const& get(Data const& d) noexcept {
if (inSitu<T>()) {
return *(std::add_pointer_t<T const>)static_cast<void const*>(&d.buff_);
} else {
return *static_cast<std::add_pointer_t<T const>>(d.pobj_);
}
}
enum class State : short { eEmpty, eInSitu, eOnHeap };
template <class T>
struct IsPolyRef : std::false_type {};
template <class T>
struct IsPolyRef<Poly<T&>> : std::true_type {};
template <class Arg, class U>
decltype(auto) convert(U&& u) {
return detail::if_constexpr(
StrictConjunction<
IsPolyRef<remove_cvref_t<U>>,
Negation<std::is_convertible<U, Arg>>>(),
[&](auto id) -> decltype(auto) {
return poly_cast<remove_cvref_t<Arg>>(id(u).get());
},
[&](auto id) -> U&& { return static_cast<U&&>(id(u)); });
}
template <class Fun>
struct IsConstMember : std::false_type {};
template <class R, class C, class... As>
struct IsConstMember<R (C::*)(As...) const> : std::true_type {};
template <class R, class C, class... As>
struct IsConstMember<R (*)(C const&, As...)> : std::true_type {};
template <class R, class C, class... As>
struct IsConstMember<R (C::*)(As...) const noexcept> : std::true_type {};
template <class R, class C, class... As>
struct IsConstMember<R (*)(C const&, As...) noexcept> : std::true_type {};
template <
class T,
auto User,
class I,
class = ArgTypes<User, I>,
class = Bool<true>>
struct ThunkFn {
template <class R, class D, class... As>
constexpr /* implicit */ operator FnPtr<R, D&, As...>() const noexcept {
return nullptr;
}
};
template <class T, auto User, class I, class... Args>
struct ThunkFn<
T,
User,
I,
TypeList<Args...>,
Bool<
!std::is_const<std::remove_reference_t<T>>::value ||
IsConstMember<decltype(User)>::value>> {
template <class R, class D, class... As>
constexpr /* implicit */ operator FnPtr<R, D&, As...>() const noexcept {
struct _ {
static R call(D& d, As... as) {
return folly::invoke(
User, get<T>(d), convert<Args>(static_cast<As&&>(as))...);
}
};
return &_::call;
}
};
template <
class I,
class = MembersOf<I, Archetype<I>>,
class = SubsumptionsOf<I>>
struct VTable;
template <class T, auto User, class I>
inline constexpr ThunkFn<T, User, I> thunk_() noexcept {
return ThunkFn<T, User, I>{};
}
template <class I>
constexpr VTable<I> const* vtable() noexcept {
return &StaticConst<VTable<I>>::value;
}
template <class I, class T>
struct VTableFor : VTable<I> {
constexpr VTableFor() noexcept : VTable<I>{Type<T>{}} {}
};
template <class I, class T>
constexpr VTable<I> const* vtableFor() noexcept {
return &StaticConst<VTableFor<I, T>>::value;
}
template <class I, class T>
constexpr void* vtableForRef(RefType ref) {
switch (ref) {
case RefType::eRvalue:
return const_cast<VTable<I>*>(vtableFor<I, T&&>());
case RefType::eLvalue:
return const_cast<VTable<I>*>(vtableFor<I, T&>());
case RefType::eConstLvalue:
return const_cast<VTable<I>*>(vtableFor<I, T const&>());
}
return nullptr;
}
template <
class I,
class T,
std::enable_if_t<std::is_reference<T>::value, int> = 0>
void* execOnHeap(Op op, Data* from, void* to) {
switch (op) {
case Op::eNuke:
break;
case Op::eMove:
case Op::eCopy:
static_cast<Data*>(to)->pobj_ = from->pobj_;
break;
case Op::eType:
return const_cast<void*>(static_cast<void const*>(&typeid(T)));
case Op::eAddr:
if (*static_cast<std::type_info const*>(to) == typeid(T)) {
return from->pobj_;
}
throw_exception<BadPolyCast>();
case Op::eRefr:
return vtableForRef<I, remove_cvref_t<T>>(
static_cast<RefType>(reinterpret_cast<std::uintptr_t>(to)));
}
return nullptr;
}
template <
class I,
class T,
std::enable_if_t<Negation<std::is_reference<T>>::value, int> = 0>
void* execOnHeap(Op op, Data* from, void* to) {
switch (op) {
case Op::eNuke:
delete &get<T>(*from);
break;
case Op::eMove:
static_cast<Data*>(to)->pobj_ = std::exchange(from->pobj_, nullptr);
break;
case Op::eCopy:
detail::if_constexpr(std::is_copy_constructible<T>(), [&](auto id) {
static_cast<Data*>(to)->pobj_ = new T(id(get<T>(*from)));
});
break;
case Op::eType:
return const_cast<void*>(static_cast<void const*>(&typeid(T)));
case Op::eAddr:
if (*static_cast<std::type_info const*>(to) == typeid(T)) {
return from->pobj_;
}
throw_exception<BadPolyCast>();
case Op::eRefr:
return vtableForRef<I, remove_cvref_t<T>>(
static_cast<RefType>(reinterpret_cast<std::uintptr_t>(to)));
}
return nullptr;
}
template <class I, class T>
void* execInSitu(Op op, Data* from, void* to) {
switch (op) {
case Op::eNuke:
get<T>(*from).~T();
break;
case Op::eMove:
::new (static_cast<void*>(&static_cast<Data*>(to)->buff_))
T(std::move(get<T>(*from)));
get<T>(*from).~T();
break;
case Op::eCopy:
detail::if_constexpr(std::is_copy_constructible<T>(), [&](auto id) {
::new (static_cast<void*>(&static_cast<Data*>(to)->buff_))
T(id(get<T>(*from)));
});
break;
case Op::eType:
return const_cast<void*>(static_cast<void const*>(&typeid(T)));
case Op::eAddr:
if (*static_cast<std::type_info const*>(to) == typeid(T)) {
return &from->buff_;
}
throw_exception<BadPolyCast>();
case Op::eRefr:
return vtableForRef<I, remove_cvref_t<T>>(
static_cast<RefType>(reinterpret_cast<std::uintptr_t>(to)));
}
return nullptr;
}
inline void* noopExec(Op op, Data*, void*) {
if (op == Op::eAddr)
throw_exception<BadPolyAccess>();
return const_cast<void*>(static_cast<void const*>(&typeid(void)));
}
template <class I>
struct BasePtr {
VTable<I> const* vptr_;
};
template <class I, class T>
constexpr void* (*getOpsImpl(std::true_type) noexcept)(Op, Data*, void*) {
return &execInSitu<I, T>;
}
template <class I, class T>
constexpr void* (*getOpsImpl(std::false_type) noexcept)(Op, Data*, void*) {
return &execOnHeap<I, T>;
}
template <class I, class T>
constexpr void* (*getOps() noexcept)(Op, Data*, void*) {
return getOpsImpl<I, T>(std::integral_constant<bool, inSitu<T>()>{});
}
template <class I, auto... Arch, class... S>
struct VTable<I, PolyMembers<Arch...>, TypeList<S...>>
: BasePtr<S>..., std::tuple<SignatureOf<Arch, I>...> {
private:
template <class T, auto... User>
constexpr VTable(Type<T>, PolyMembers<User...>) noexcept
: BasePtr<S>{vtableFor<S, T>()}...,
std::tuple<SignatureOf<Arch, I>...>{thunk_<T, User, I>()...},
state_{inSitu<T>() ? State::eInSitu : State::eOnHeap},
ops_{getOps<I, T>()} {}
public:
constexpr VTable() noexcept
: BasePtr<S>{vtable<S>()}...,
std::tuple<SignatureOf<Arch, I>...>{
static_cast<SignatureOf<Arch, I>>(throw_())...},
state_{State::eEmpty},
ops_{&noopExec} {}
template <class T>
explicit constexpr VTable(Type<T>) noexcept
: VTable{Type<T>{}, MembersOf<I, T>{}} {}
State state_;
void* (*ops_)(Op, Data*, void*);
std::tuple<SignatureOf<Arch, I>...>& tuple() { return *this; }
const std::tuple<SignatureOf<Arch, I>...>& tuple() const { return *this; }
};
template <class I>
constexpr VTable<I> const& select(VTable<_t<Type<I>>> const& vtbl) noexcept {
return vtbl;
}
template <class I>
constexpr VTable<I> const& select(BasePtr<_t<Type<I>>> const& base) noexcept {
return *base.vptr_;
}
struct PolyAccess {
template <std::size_t N, typename This, typename... As>
static auto call(This&& _this, As&&... args)
-> decltype(static_cast<This&&>(_this).template _polyCall_<N>(
static_cast<As&&>(args)...)) {
static_assert(
!IsInstanceOf<std::decay_t<This>, Poly>::value,
"When passing a Poly<> object to call(), you must explicitly "
"say which Interface to dispatch to, as in "
"call<0, MyInterface>(self, args...)");
return static_cast<This&&>(_this).template _polyCall_<N>(
static_cast<As&&>(args)...);
}
template <class Poly>
using Iface = typename remove_cvref_t<Poly>::_polyInterface_;
template <class Node, class Tfx = MetaIdentity>
static typename remove_cvref_t<Node>::template _polySelf_<Node, Tfx> self_();
template <class T, class Poly, class I = Iface<Poly>>
static decltype(auto) cast(Poly&& _this) {
using Ret = AddCvrefOf<AddCvrefOf<T, I>, Poly&&>;
return static_cast<Ret>(
*static_cast<std::add_pointer_t<Ret>>(_this.vptr_->ops_(
Op::eAddr,
const_cast<Data*>(static_cast<Data const*>(&_this)),
const_cast<void*>(static_cast<void const*>(&typeid(T))))));
}
template <class Poly>
static decltype(auto) root(Poly&& _this) noexcept {
return static_cast<Poly&&>(_this)._polyRoot_();
}
template <class I>
static std::type_info const& type(PolyRoot<I> const& _this) noexcept {
return *static_cast<std::type_info const*>(
_this.vptr_->ops_(Op::eType, nullptr, nullptr));
}
template <class I>
static VTable<remove_cvref_t<I>> const* vtable(
PolyRoot<I> const& _this) noexcept {
return _this.vptr_;
}
template <class I>
static Data* data(PolyRoot<I>& _this) noexcept {
return &_this;
}
template <class I>
static Data const* data(PolyRoot<I> const& _this) noexcept {
return &_this;
}
template <class I>
static Poly<I&&> move(PolyRoot<I&> const& _this) noexcept {
return Poly<I&&>{_this, Type<I&>{}};
}
template <class I>
static Poly<I const&> move(PolyRoot<I const&> const& _this) noexcept {
return Poly<I const&>{_this, Type<I const&>{}};
}
};
template <class I, class Tail>
struct PolyNode : Tail {
private:
friend PolyAccess;
using Tail::Tail;
template <std::size_t K, typename... As>
decltype(auto) _polyCall_(As&&... as) {
// Convert VTable to tuple explicitly to workaround an MSVC bug.
return std::get<K>(select<I>(*PolyAccess::vtable(*this)).tuple())(
*PolyAccess::data(*this), static_cast<As&&>(as)...);
}
template <std::size_t K, typename... As>
decltype(auto) _polyCall_(As&&... as) const {
return std::get<K>(select<I>(*PolyAccess::vtable(*this)).tuple())(
*PolyAccess::data(*this), static_cast<As&&>(as)...);
}
};
struct MakePolyNode {
template <class I, class State>
using apply = InterfaceOf<I, PolyNode<I, State>>;
};
template <class I>
struct PolyRoot : private PolyBase, private Data {
friend PolyAccess;
friend Poly<I>;
friend PolyVal<I>;
friend PolyRef<I>;
template <class Node, class Tfx>
using _polySelf_ = Poly<AddCvrefOf<MetaApply<Tfx, I>, Node>>;
using _polyInterface_ = I;
private:
PolyRoot& _polyRoot_() noexcept { return *this; }
PolyRoot const& _polyRoot_() const noexcept { return *this; }
VTable<std::decay_t<I>> const* vptr_ = vtable<std::decay_t<I>>();
};
template <class I>
using PolyImpl = TypeFold<
InclusiveSubsumptionsOf<remove_cvref_t<I>>,
PolyRoot<I>,
MakePolyNode>;
// A const-qualified function type means the user is trying to disambiguate
// a member function pointer.
template <class Fun> // Fun = R(As...) const
struct Sig {
template <class T>
constexpr Fun T::*operator()(Fun T::*t) const /* nolint */ volatile noexcept {
return t;
}
template <class F, class T>
constexpr F T::*operator()(F T::*t) const /* nolint */ volatile noexcept {
return t;
}
};
// A function type with no arguments means the user is trying to disambiguate
// a member function pointer.
template <class R>
struct Sig<R()> : Sig<R() const> {
using Fun = R();
using Sig<R() const>::operator();
template <class T>
constexpr Fun T::*operator()(Fun T::*t) const noexcept {
return t;
}
};
template <class R, class... As>
struct SigImpl : Sig<R(As...) const> {
using Fun = R(As...);
using Sig<R(As...) const>::operator();
template <class T>
constexpr Fun T::*operator()(Fun T::*t) const noexcept {
return t;
}
constexpr Fun* operator()(Fun* t) const noexcept { return t; }
template <class F>
constexpr F* operator()(F* t) const noexcept {
return t;
}
};
// The user could be trying to disambiguate either a member or a free function.
template <class R, class... As>
struct Sig<R(As...)> : SigImpl<R, As...> {};
// This case is like the one above, except we want to add an overload that
// handles the case of a free function where the first argument is more
// const-qualified than the user explicitly specified.
template <class R, class A, class... As>
struct Sig<R(A&, As...)> : SigImpl<R, A&, As...> {
using CCFun = R(A const&, As...);
using SigImpl<R, A&, As...>::operator();
constexpr CCFun* operator()(CCFun* t) const /* nolint */ volatile noexcept {
return t;
}
};
template <bool>
struct ModelsInterfaceFalse0_;
template <>
struct ModelsInterfaceFalse0_<false> {
template <typename... T>
using apply = std::bool_constant<(!require_sizeof<T> || ...)>;
};
template <>
struct ModelsInterfaceFalse0_<true> {
template <typename...>
using apply = std::false_type;
};
template <typename... T>
using ModelsInterfaceFalse_ = typename ModelsInterfaceFalse0_<(
std::is_function_v<remove_cvref_t<T>> || ...)>::template apply<T...>;
template <class T, class I, class = void>
struct ModelsInterface2_ : ModelsInterfaceFalse_<T, I> {};
template <class T, class I>
struct ModelsInterface2_<
T,
I,
void_t<
std::enable_if_t<
std::is_constructible<AddCvrefOf<std::decay_t<T>, I>, T>::value>,
MembersOf<std::decay_t<I>, std::decay_t<T>>>> : std::true_type {};
template <class T, class I, class = void>
struct ModelsInterface_ : ModelsInterfaceFalse_<T, I> {};
template <class T, class I>
struct ModelsInterface_<
T,
I,
std::enable_if_t<
Negation<std::is_base_of<PolyBase, std::decay_t<T>>>::value>>
: ModelsInterface2_<T, I> {};
template <class T, class I>
struct ModelsInterface : ModelsInterface_<T, I> {};
template <class I1, class I2>
struct ValueCompatible : std::is_base_of<I1, I2> {};
// This prevents PolyRef's converting constructors and assignment operators
// from being considered as copy constructors and assignment operators:
template <class I1>
struct ValueCompatible<I1, I1> : std::false_type {};
template <class I1, class I2, class I2Ref>
struct ReferenceCompatible : std::is_constructible<I1, I2Ref> {};
// This prevents PolyRef's converting constructors and assignment operators
// from being considered as copy constructors and assignment operators:
template <class I1, class I2Ref>
struct ReferenceCompatible<I1, I1, I2Ref> : std::false_type {};
} // namespace detail
/// \endcond
} // namespace folly
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