https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102721
Bug ID: 102721 Summary: out-of-line member function definition fails to allow lambda in unevaluated-context of new feature in c++20 Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: nickhuang99 at hotmail dot com Target Milestone: --- The following snippet code exposes that GCC parser doesn't comply with c++20 standard to allow lambda in unevaluated context. It seems this out-of-line definition creates a new lambda type where lambda as operand of "decltype" should be treated as in unevaluated context. So, it shouldn't create a new lambda type in out-of-line definition. Both clang and MSVC++ (https://www.godbolt.org/z/EMbb44fd8) parse this correctly. (with "-std=c++20") template<class T> struct A { void foo(const T){} }; template<> void A<decltype(+[]{})[3]>::foo(const decltype(+[]{})[3]) {} <source>:9:6: error: ambiguating new declaration of 'void A<void (* [3])()>::foo(void (* const*)())' 9 | void A<decltype(+[]{})[3]>::foo(const decltype(+[]{})[3]) | ^~~~~~~~~~~~~~~~~~~~~ <source>:5:10: note: old declaration 'void A<T>::foo(T) [with T = void (* [3])()]' 5 | void foo(const T){} | ^~~