http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54864
Bug #: 54864 Summary: Decltype in nested class Classification: Unclassified Product: gcc Version: 4.8.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ AssignedTo: unassig...@gcc.gnu.org ReportedBy: zeratul...@hotmail.com The following code: struct S { int foo(); struct nested { S* outer; auto bar() -> decltype(outer->foo()); }; }; fails to compile with the following errors: test.cpp:9:37: error: invalid use of incomplete type 'struct S' auto bar() -> decltype(outer->foo()); ^ test.cpp:1:8: error: forward declaration of 'struct S' struct S ^ test.cpp:9:37: error: invalid use of incomplete type 'struct S' auto bar() -> decltype(outer->foo()); ^ test.cpp:1:8: error: forward declaration of 'struct S' struct S ^ I believe this code is valid. It is accepted by clang trunk. Tested with gcc-4.8-20121007.