| Message ID | 20240620153641.2024863-1-jwakely@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | libstdc++: Make std::any_cast<void> ill-formed (LWG 3305) | expand |
Pushed to trunk now. I might backport this later too. On Thu, 20 Jun 2024 at 16:39, Jonathan Wakely <jwakely@redhat.com> wrote: > > Tested x86_64-linux. > > -- >8 -- > > LWG 3305 was approved earlier this year in Tokyo. We need to give an > error if using std::any_cast<void>, but std::any_cast<void()> is valid > (but always returns null). > > libstdc++-v3/ChangeLog: > > * include/std/any (any_cast(any*), any_cast(const any*)): Add > static assertion to reject void types, as per LWG 3305. > * testsuite/20_util/any/misc/lwg3305.cc: New test. > --- > libstdc++-v3/include/std/any | 8 ++++++++ > .../testsuite/20_util/any/misc/lwg3305.cc | 15 +++++++++++++++ > 2 files changed, 23 insertions(+) > create mode 100644 libstdc++-v3/testsuite/20_util/any/misc/lwg3305.cc > > diff --git a/libstdc++-v3/include/std/any b/libstdc++-v3/include/std/any > index 690ddc2aa57..e4709b1ce04 100644 > --- a/libstdc++-v3/include/std/any > +++ b/libstdc++-v3/include/std/any > @@ -554,6 +554,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > template<typename _ValueType> > inline const _ValueType* any_cast(const any* __any) noexcept > { > + // _GLIBCXX_RESOLVE_LIB_DEFECTS > + // 3305. any_cast<void> > + static_assert(!is_void_v<_ValueType>); > + > + // As an optimization, don't bother instantiating __any_caster for > + // function types, since std::any can only hold objects. > if constexpr (is_object_v<_ValueType>) > if (__any) > return static_cast<_ValueType*>(__any_caster<_ValueType>(__any)); > @@ -563,6 +569,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > template<typename _ValueType> > inline _ValueType* any_cast(any* __any) noexcept > { > + static_assert(!is_void_v<_ValueType>); > + > if constexpr (is_object_v<_ValueType>) > if (__any) > return static_cast<_ValueType*>(__any_caster<_ValueType>(__any)); > diff --git a/libstdc++-v3/testsuite/20_util/any/misc/lwg3305.cc b/libstdc++-v3/testsuite/20_util/any/misc/lwg3305.cc > new file mode 100644 > index 00000000000..49f5d747ab3 > --- /dev/null > +++ b/libstdc++-v3/testsuite/20_util/any/misc/lwg3305.cc > @@ -0,0 +1,15 @@ > +// { dg-do compile { target c++17 } } > + > +// LWG 3305. any_cast<void> > + > +#include <any> > + > +void > +test_lwg3305() > +{ > + std::any a; > + (void) std::any_cast<const void>(&a); // { dg-error "here" } > + const std::any a2; > + (void) std::any_cast<volatile void>(&a2); // { dg-error "here" } > +} > +// { dg-error "static assertion failed" "" { target *-*-* } 0 } > -- > 2.45.2 >
diff --git a/libstdc++-v3/include/std/any b/libstdc++-v3/include/std/any index 690ddc2aa57..e4709b1ce04 100644 --- a/libstdc++-v3/include/std/any +++ b/libstdc++-v3/include/std/any @@ -554,6 +554,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION template<typename _ValueType> inline const _ValueType* any_cast(const any* __any) noexcept { + // _GLIBCXX_RESOLVE_LIB_DEFECTS + // 3305. any_cast<void> + static_assert(!is_void_v<_ValueType>); + + // As an optimization, don't bother instantiating __any_caster for + // function types, since std::any can only hold objects. if constexpr (is_object_v<_ValueType>) if (__any) return static_cast<_ValueType*>(__any_caster<_ValueType>(__any)); @@ -563,6 +569,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION template<typename _ValueType> inline _ValueType* any_cast(any* __any) noexcept { + static_assert(!is_void_v<_ValueType>); + if constexpr (is_object_v<_ValueType>) if (__any) return static_cast<_ValueType*>(__any_caster<_ValueType>(__any)); diff --git a/libstdc++-v3/testsuite/20_util/any/misc/lwg3305.cc b/libstdc++-v3/testsuite/20_util/any/misc/lwg3305.cc new file mode 100644 index 00000000000..49f5d747ab3 --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/any/misc/lwg3305.cc @@ -0,0 +1,15 @@ +// { dg-do compile { target c++17 } } + +// LWG 3305. any_cast<void> + +#include <any> + +void +test_lwg3305() +{ + std::any a; + (void) std::any_cast<const void>(&a); // { dg-error "here" } + const std::any a2; + (void) std::any_cast<volatile void>(&a2); // { dg-error "here" } +} +// { dg-error "static assertion failed" "" { target *-*-* } 0 }