[cfe-dev] Problem with default member initialization and noexcept default constructor
Dimitry Andric via cfe-dev
cfe-dev at lists.llvm.org
Tue Jul 11 11:55:38 PDT 2017
Richard has posted a much nicer variant already. :)
-Dimitry
> On 11 Jul 2017, at 20:54, Joe Sylve <joe.sylve at gmail.com> wrote:
>
> Please note this on the bug report
>
>
> On Tue, Jul 11, 2017, 13:46 Dimitry Andric <dimitry at andric.com> wrote:
> The shortest reduction I could come up with is this:
>
> template <bool> struct a;
> template <class> struct B {};
> template <class b, bool = B<b>::f> struct g;
> template <class c, class, int = g<c>::f> struct i;
> template <class> class j {
> public:
> j();
> template <class d> j(j<d>, typename a<i<d *, int *>::f>::e = int());
> };
> struct k {
> k() noexcept = default;
> k(k &) = default;
> j<int> h{};
> };
>
> All versions of g++ that I tried compile this without error, while clang says:
>
> testcase.cpp:11:3: error: default member initializer for 'h' needed within definition of enclosing class 'k' outside of member functions
> k() noexcept = default;
> ^
> testcase.cpp:3:27: note: in instantiation of template class 'B<int *>' requested here
> template <class b, bool = B<b>::f> struct g;
> ^
> testcase.cpp:4:33: note: in instantiation of default argument for 'g<int *>' required here
> template <class c, class, int = g<c>::f> struct i;
> ^~~~
> testcase.cpp:8:41: note: in instantiation of default argument for 'i<int *, int *>' required here
> template <class d> j(j<d>, typename a<i<d *, int *>::f>::e = int());
> ^~~~~~~~~~~~~
> testcase.cpp:5:24: note: while substituting deduced template arguments into function template 'j' [with d = int]
> template <class> class j {
> ^
> testcase.cpp:13:10: note: default member initializer declared here
> j<int> h{};
> ^
> 1 error generated.
>
> -Dimitry
>
> > On 11 Jul 2017, at 16:54, Joe Sylve <joe.sylve at gmail.com> wrote:
> >
> > It is, but I'm not sure that libc++ is the cause or just points out the bug. If you look at the stack overflow link, you'll see an example of different code that triggers a similar error without the use of any library stuff.
> >
> >
> > On Tue, Jul 11, 2017, 03:45 Dimitry Andric <dimitry at andric.com> wrote:
> > FYI, this looks like an issue in libc++. If I compile your sample with the latest and greatest clang, but point it to the g++ 7.1.1 libstdc++ headers, it works just fine.
> >
> > -Dimitry
> >
> >> On 10 Jul 2017, at 20:55, Joe Sylve via cfe-dev <cfe-dev at lists.llvm.org> wrote:
> >>
> >> I'm seeing an error that is similar to the question raised at https://stackoverflow.com/questions/43819314. That question seems to not have any consensus as to what the problem may be.
> >>
> >> I would appreciate if someone could shed some light on my issue and let me know if this is a known compiler bug or if clang is working as intended.
> >>
> >> The following code produces a compile-time error in clang++ 4.0.0 and later, but works fine in gcc as well as previous versions of clang.
> >>
> >> #include <memory>
> >>
> >> struct A {
> >> A() noexcept = default;
> >> A(const A&) noexcept = default;
> >>
> >> std::shared_ptr<int> _a {};
> >> };
> >>
> >> int main() {
> >> return 0;
> >> }
> >>
> >> It's worth noting that if I remove the copy constructor, this compiles fine. If I remove the noexcept qualification from the default constructor it also compiles fine.
> >>
> >> The error I'm getting is as follows:
> >>
> >> <source>:4:5: error: default member initializer for '_a' needed within definition of enclosing class 'A' outside of member functions
> >> A() noexcept = default;
> >> ^
> >> /opt/compiler-explorer/clang-4.0.0/bin/../include/c++/v1/type_traits:1306:29: note: in instantiation of template class 'std::__1::is_class<int *>' requested here
> >> template <class _Tp, bool = is_class<_Tp>::value>
> >> ^
> >> /opt/compiler-explorer/clang-4.0.0/bin/../include/c++/v1/type_traits:1311:71: note: in instantiation of default argument for '__libcpp_abstract<int *>' required here
> >> template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_abstract : public __libcpp_abstract<_Tp> {};
> >> ^~~~~~~~~~~~~~~~~~~~~~
> >> /opt/compiler-explorer/clang-4.0.0/bin/../include/c++/v1/type_traits:1384:39: note: in instantiation of template class 'std::__1::is_abstract<int *>' requested here
> >> !is_abstract<_T2>::value> {};
> >> ^
> >> /opt/compiler-explorer/clang-4.0.0/bin/../include/c++/v1/memory:3918:39: note: in instantiation of template class 'std::__1::is_convertible<int *, int *>' requested here
> >> typename enable_if<is_convertible<_Yp*, element_type*>::value, __nat>::type = __nat())
> >> ^
> >> /opt/compiler-explorer/clang-4.0.0/bin/../include/c++/v1/memory:3883:28: note: while substituting deduced template arguments into function template 'shared_ptr' [with _Yp = int]
> >> class _LIBCPP_TEMPLATE_VIS shared_ptr
> >> ^
> >> <source>:7:26: note: default member initializer declared here
> >> std::shared_ptr<int> _a {};
> >> _______________________________________________
> >> cfe-dev mailing list
> >> cfe-dev at lists.llvm.org
> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
> >
>
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