In the section "11.9 Member access control" of the C++20 Standard there is provided an example (p.#7, example #2) of using a protected inner class of a class as a base class for a derived class and the corresponding text relative to such a declaration.

Here is a simplified by me version of the example

class A {
//...
protected:
    struct B { };
};

struct D: A::B, A { };

And there is written

Similarly, the use of A::B as a base-specifier is well-formed because D is derived from A, so checking of base-specifiers must be deferred until the entire base-specifier-list has been seen.

However  this declaration

struct D: A::B, A { };

is compiled by neither for example x86-64 clang (trunk) nor by MS VS C++ with its last version of the compiler.

 

if to change the declaration like

 

struct D: A, A::B { }; 

 

then the MS VS C++ compiler compiles the declaration. However the compiler x86-64 clang (trunk)  still does not compile the declaration. 

 

is it a bug of the compilers?

 

With best regards,

(Vlad from Moscow)

 

You can meet me at http://cpp.forum24.ru/ or www.stackoverflow.com or http://ru.stackoverflow.com

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