c++ - Using "using" twice interpreted differently by different compilers -

consider following code:

struct {     int propose(); };  struct a1 : {     int propose(int);     using a::propose; };  struct b1 : a1 { protected:     using a1::propose; public:     using a::propose; };  int main() {     b1().propose(); } 

let's compile this: g++ -std=c++11 main.cpp.

i'm getting following compiler error using gnu 4.8.1:

main.cpp: in function 'int main()':                                                                                                                     main.cpp:2:9: error: 'int a::propose()' inaccessible      int propose();          ^ main.cpp:18:18: error: within context      b1().propose(); 

however, code compiles in appleclang 6.0.0.6000056.

i understand there no need using in b1, (in code necessary, had 1 using mistake). in case, why clang compiles it? expected?

in [namespace.udecl], have:

when using-declaration brings names base class derived class scope, member functions , member function templates in derived class override and/or hide member functions , member function templates same name, parameter-type-list (8.3.5), cv-qualification, , ref-qualifier (if any) in base class (rather conflicting).

the standard explicitly says names brought in not conflict names in base class. doesn't bringing in conflicting names.

the section says:

a using-declaration declaration , can therefore used repeatedly (and where) multiple declarations allowed. [ example:

struct b {     int i; };  struct x : b {     using b::i;     using b::i; // error: double member declaration }; 

—end example ]

and interestingly, in following example it's gcc happily compiles (and prints a) while clang allows construction of c rejects call foo ambiguous:

struct {     void foo() { std::cout << "a\n"; } };  struct b {     void foo() { std::cout << "b\n"; } };  struct c : a, b {     using a::foo;     using b::foo; };   int main() {     c{}.foo();     return 0; } 

so short answer - suspect underspecified in standard , both compilers doing acceptable things. avoid writing sort of code general sanity.