private forward declare, public class. What does the standard say?

[Daniel T.]

class A {
class B;
// ... later in the code
public:
class B { };
};

I have one compiler telling me that class A::B is inaccessible outside
of A, and another compiler accesses it just fine. Which is correct
according to the standard?

 

[Kai-Uwe Bux]

class A {
class B;
// ... later in the code
public:
class B { };
};

I have one compiler telling me that class A::B is inaccessible outside
of A, and another compiler accesses it just fine. Which is correct
according to the standard?

Both. Your program is ill-formed. 11.1/3:

"When a member is redeclared within its class definition, the access
specified at its redeclaration shall be the same as at its initial
declaration. [Example:
struct S {
class A;
private:
class A { }; // error: cannot change access
};
-end example]"

Since your program is ill-formed, the compiler is free to compile it
as it sees fit.

Just a nit: that looks like a diagnosable rule to me, in which case the
compiler has to issue a diagnostic as per [1.4/2] and _then_ can go on an
compile the program anyway as per [1.4/8].


Best

Kai-Uwe Bux