https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70845
--- Comment #4 from Wei-Wei Tu <tuwwcn at gmail dot com> --- (In reply to Jonathan Wakely from comment #3) > (In reply to Wei-Wei Tu from comment #2) > > This is the test case > > Yes, I know, I already added it in comment 1 :-) > > Preprocessed source from gcc-5 fails, so this is due to some front-end > change (either getting stricter and diagnosing something bad in the library > headers, or a new FE bug). This is my first time to report a bug. I'm so sorry for missing the headers. Is the code valid according to the language standard? (I'm not so sure about it.) This is the words about c++17 inherited constructors referred by using-declarations(from cppreference): If the using-declaration refers to a constructor of a direct base of the class being defined (e.g. using Base::Base;), all constructors of that base (ignoring member access) are made visible to overload resolution when initializing the derived class. If overload resolution selects an inherited constructor, it is accessible if it would be accessible when used to construct an object of the corresponding base class: the accessibility of the using-declaration that introduced it is ignored. If overload resolution selects one of the inherited constructors when initializing an object of such derived class, then the Base subobject from which the constructor was inherited is initialized using the inherited constructor, and all other bases and members of Derived are initialized as if by the defaulted default constructor (default member initializers are used if provided, otherwise default initialization takes place). The entire initialization is treated as a single function call: initialization of the parameters of the inherited constructor is sequenced-before initialization of any base or member of the derived object. As with using-declarations for any other non-static member functions, if an inherited constructor matches the signature of one of the constructors of Derived, it is hidden from lookup by the version found in Derived. If one of the inherited constructors of Base happens to have the signature that matches a copy/move constructor of the Derived, it does not prevent implicit generation of Derived copy/move constructor (which then hides the inherited version, similar to using operator=).
