https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87748
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed|2018-10-25 00:00:00 |2019-4-16
Known to fail|9.0 |
--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Another reproducer from PR 90080:
struct false_type { static constexpr bool value = false; };
struct true_type { static constexpr bool value = true; };
template<bool, typename = void> struct enable_if { };
template<typename T> struct enable_if<true, T> { using type = T; };
template<typename T> T&& declval();
template<typename T, typename U, typename = U>
struct is_static_castable : false_type
{};
template<typename T, typename U>
struct is_static_castable<T, U, decltype(static_cast<U>(declval<T>()))> :
true_type
{};
template<typename To, typename From, typename
enable_if<is_static_castable<From*, To*>::value, int>::type = 0>
To* safePtrCast(From* from)
{
return static_cast<To*>(from);
}
template<typename To, typename From, typename
enable_if<!is_static_castable<From*, To*>::value, int>::type = 0>
To* safePtrCast(From* from)
{
return dynamic_cast<To*>(from);
}
struct BarBase{ virtual ~BarBase() = default;};
struct Bar : virtual BarBase{};
Bar* foo(BarBase* b){
return safePtrCast<Bar>(b);
}
90080.cc: In instantiation of ‘struct is_static_castable<BarBase*, Bar*,
Bar*>’:
90080.cc:21:57: required by substitution of ‘template<class To, class From,
typename enable_if<(! is_static_castable<From*, To*>::value), int>::type
<anonymous> > To* safePtrCast(From*) [with To = Bar; From = BarBase; typename
enable_if<(! is_static_castable<From*, To*>::value), int>::type <anonymous> =
<missing>]’
90080.cc:31:30: required from here
90080.cc:12:42: error: cannot convert from pointer to base class ‘BarBase’ to
pointer to derived class ‘Bar’ because the base is virtual
12 | struct is_static_castable<T, U, decltype(static_cast<U>(declval<T>()))>
: true_type
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
90080.cc:12:42: error: cannot convert from pointer to base class ‘BarBase’ to
pointer to derived class ‘Bar’ because the base is virtual
90080.cc: In instantiation of ‘To* safePtrCast(From*) [with To = Bar; From =
BarBase; typename enable_if<is_static_castable<From*, To*>::value, int>::type
<anonymous> = 0]’:
90080.cc:31:30: required from here
90080.cc:18:12: error: cannot convert from pointer to base class ‘BarBase’ to
pointer to derived class ‘Bar’ because the base is virtual
18 | return static_cast<To*>(from);
| ^~~~~~~~~~~~~~~~~~~~~~
