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Fix building with MSVC:
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* If `!__cpp_aggregate_bases`, avoid a lambda in an initializer of a static
  constexpr variable. Call a private static constexpr function instead.

* If `!__cpp_aggregate_bases`, do not construct a struct from a base struct.
  Assign to the base class with a cast.

* In `Initializer` base classes, make `kMethodsDefault` a template with a dummy
  parameter, so that it is instantiated only when needed, which prevents
  breaking the build if the target type is not default-constructible.

PiperOrigin-RevId: 630410305
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@QrczakMK
QrczakMK committed May 3, 2024
1 parent f976536 commit 02482f2
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Showing 2 changed files with 98 additions and 47 deletions.
135 changes: 91 additions & 44 deletions riegeli/base/initializer.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -110,6 +110,7 @@ class InitializerBase {
InitializerBase(InitializerBase&& other) = default;
InitializerBase& operator=(InitializerBase&&) = delete;

template <typename Dummy = void>
static constexpr Methods kMethodsDefault = {ConstructMethodDefault};

template <typename Arg>
Expand Down Expand Up @@ -185,8 +186,9 @@ class InitializerValueBase : public InitializerBase<T> {
};

#if __cpp_aggregate_bases
template <typename Dummy = void>
static constexpr Methods kMethodsDefault = {
InitializerValueBase::InitializerBase::kMethodsDefault,
InitializerValueBase::InitializerBase::template kMethodsDefault<>,
ReferenceMethodDefault};

template <typename Arg>
Expand All @@ -212,47 +214,68 @@ class InitializerValueBase : public InitializerBase<T> {
Args...>,
ReferenceMethodFromTuple<Args...>};
#else
static constexpr Methods kMethodsDefault = [] {
Methods methods(InitializerValueBase::InitializerBase::kMethodsDefault);
static constexpr Methods MakeMethodsDefault() {
Methods methods;
static_cast<typename InitializerValueBase::InitializerBase::Methods&>(
methods) =
InitializerValueBase::InitializerBase::template kMethodsDefault<>;
methods.reference = ReferenceMethodDefault;
return methods;
}();
}
template <typename Dummy = void>
static constexpr Methods kMethodsDefault = MakeMethodsDefault();

template <typename Arg>
static constexpr Methods kMethodsFromObject = [] {
Methods methods(
InitializerValueBase::InitializerBase::template kMethodsFromObject<
Arg>);
static constexpr Methods MakeMethodsFromObject() {
Methods methods;
static_cast<typename InitializerValueBase::InitializerBase::Methods&>(
methods) =
InitializerValueBase::InitializerBase::template kMethodsFromObject<Arg>;
methods.reference = ReferenceMethodFromObject<Arg>;
return methods;
}();
}
template <typename Arg>
static constexpr Methods kMethodsFromObject = MakeMethodsFromObject<Arg>();

template <typename... Args>
static constexpr Methods kMethodsFromMaker = [] {
Methods methods(
static constexpr Methods MakeMethodsFromMaker() {
Methods methods;
static_cast<typename InitializerValueBase::InitializerBase::Methods&>(
methods) =
InitializerValueBase::InitializerBase::template kMethodsFromMaker<
Args...>);
Args...>;
methods.reference = ReferenceMethodFromMaker<Args...>;
return methods;
}();
}
template <typename... Args>
static constexpr Methods kMethodsFromMaker = MakeMethodsFromMaker<Args...>();

template <typename... Args>
static constexpr Methods kMethodsFromConstMaker = [] {
Methods methods(
static constexpr Methods MakeMethodsFromConstMaker() {
Methods methods;
static_cast<typename InitializerValueBase::InitializerBase::Methods&>(
methods) =
InitializerValueBase::InitializerBase::template kMethodsFromConstMaker<
Args...>);
Args...>;
methods.reference = ReferenceMethodFromConstMaker<Args...>;
return methods;
}();
}
template <typename... Args>
static constexpr Methods kMethodsFromConstMaker =
MakeMethodsfromConstMaker<Args...>();

template <typename... Args>
static constexpr Methods kMethodsFromTuple = [] {
Methods methods(
static constexpr Methods MakeMethodsFromTuple() {
Methods methods;
static_cast<typename InitializerValueBase::InitializerBase::Methods&>(
methods) =
InitializerValueBase::InitializerBase::template kMethodsFromTuple<
Args...>);
Args...>;
methods.reference = ReferenceMethodFromTuple<Args...>;
return methods;
}();
}
template <typename... Args>
static constexpr Methods kMethodsFromTuple = MakeMethodsFromTuple<Args...>();
#endif

explicit InitializerValueBase(const Methods* methods)
Expand Down Expand Up @@ -317,8 +340,10 @@ class InitializerAssignableValueBase : public InitializerValueBase<T> {
};

#if __cpp_aggregate_bases
template <typename Dummy = void>
static constexpr Methods kMethodsDefault = {
InitializerAssignableValueBase::InitializerValueBase::kMethodsDefault,
InitializerAssignableValueBase::InitializerValueBase::
template kMethodsDefault<>,
AssignToMethodDefault};

template <typename Arg>
Expand All @@ -345,44 +370,65 @@ class InitializerAssignableValueBase : public InitializerValueBase<T> {
template kMethodsFromTuple<Args...>,
AssignToMethodFromTuple<Args...>};
#else
static constexpr Methods kMethodsDefault = [] {
Methods methods(
InitializerAssignableValueBase::InitializerValueBase::kMethodsDefault);
static constexpr Methods MakeMethodsDefault() {
Methods methods;
static_cast<typename InitializerAssignableValueBase::InitializerValueBase::
Methods&>(methods) = InitializerAssignableValueBase::
InitializerValueBase::template kMethodsDefault<>;
methods.assign_to = AssignToMethodDefault;
return methods;
}();
}
template <typename Dummy = void>
static constexpr Methods kMethodsDefault = MakeMethodsDefault();

template <typename Arg>
static constexpr Methods kMethodsFromObject = [] {
Methods methods(InitializerAssignableValueBase::InitializerValueBase::
template kMethodsFromObject<Arg>);
static constexpr Methods MakeMethodsFromObject() {
Methods methods;
static_cast<typename InitializerAssignableValueBase::InitializerValueBase::
Methods&>(methods) = InitializerAssignableValueBase::
InitializerValueBase::template kMethodsFromObject<Arg>;
methods.assign_to = AssignToMethodFromObject<Arg>;
return methods;
}();
}
template <typename Arg>
static constexpr Methods kMethodsFromObject = MakeMethodsFromObject<Arg>();

template <typename... Args>
static constexpr Methods kMethodsFromMaker = [] {
Methods methods(InitializerAssignableValueBase::InitializerValueBase::
template kMethodsFromMaker<Args...>);
static constexpr Methods MakeMethodsFromMaker() {
Methods methods;
static_cast<typename InitializerAssignableValueBase::InitializerValueBase::
Methods&>(methods) = InitializerAssignableValueBase::
InitializerValueBase::template kMethodsFromMaker<Args...>;
methods.assign_to = AssignToMethodFromMaker<Args...>;
return methods;
}();
}
template <typename... Args>
static constexpr Methods kMethodsFromMaker = MakeMethodsFromMaker<Args...>();

template <typename... Args>
static constexpr Methods kMethodsFromConstMaker = [] {
Methods methods(InitializerAssignableValueBase::InitializerValueBase::
template kMethodsFromConstMaker<Args...>);
static constexpr Methods MakeMethodsFromConstMaker() {
Methods methods;
static_cast<typename InitializerAssignableValueBase::InitializerValueBase::
Methods&>(methods) = InitializerAssignableValueBase::
InitializerValueBase::template kMethodsFromConstMaker<Args...>;
methods.assign_to = AssignToMethodFromConstMaker<Args...>;
return methods;
}();
}
template <typename... Args>
static constexpr Methods kMethodsFromConstMaker =
MakeMethodsFromConstMaker<Args...>();

template <typename... Args>
static constexpr Methods kMethodsFromTuple = [] {
Methods methods(InitializerAssignableValueBase::InitializerValueBase::
template kMethodsFromTuple<Args...>);
static constexpr Methods MakeMethodsFromTuple() {
Methods methods;
static_cast<typename InitializerAssignableValueBase::InitializerValueBase::
Methods&>(methods) = InitializerAssignableValueBase::
InitializerValueBase::template kMethodsFromTuple<Args...>;
methods.assign_to = AssignToMethodFromTuple<Args...>;
return methods;
}();
}
template <typename... Args>
static constexpr Methods kMethodsFromTuple = MakeMethodsFromTuple<Args...>();
#endif

explicit InitializerAssignableValueBase(const Methods* methods)
Expand Down Expand Up @@ -455,7 +501,8 @@ class Initializer
int> = 0>
Initializer()
: Initializer::InitializerAssignableValueBase(
&Initializer::InitializerAssignableValueBase::kMethodsDefault) {}
&Initializer::InitializerAssignableValueBase::
template kMethodsDefault<>) {}

// Constructs `Initializer<T>` from a value convertible to `T`.
template <
Expand Down Expand Up @@ -566,7 +613,7 @@ class Initializer<T, allow_explicit,
int> = 0>
Initializer()
: Initializer::InitializerValueBase(
&Initializer::InitializerValueBase::kMethodsDefault) {}
&Initializer::InitializerValueBase::template kMethodsDefault<>) {}

// Constructs `Initializer<T>` from a value convertible to `T`.
template <
Expand Down
10 changes: 7 additions & 3 deletions riegeli/digests/digester_handle.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -499,11 +499,15 @@ class DigesterHandle : public DigesterBaseHandle {
DigestMethod<T>};
#else
template <typename T>
static constexpr Methods kMethods = [] {
Methods methods(DigesterBaseHandle::kMethods<T>);
static constexpr Methods MakeMethods() {
Methods methods;
static_cast<DigesterBaseHandle::Methods&>(methods) =
DigesterBaseHandle::kMethods<T>;
methods.digest = DigestMethod<T>;
return methods;
}();
}
template <typename T>
static constexpr Methods kMethods = MakeMethods<T>();
#endif

const Methods* methods() const {
Expand Down

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