http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54359
Bug #: 54359
Summary: [C++0x][N3282] decltype in member function's trailing
return type when defined outside of class
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: bruno-...@defraine.net
Even after closing bug #49003, there remain problems regarding the handling of
N3282 (resolution of DR 1207). Specifically, the problems have to do with a
definition of a member function outside of the class.
Consider these test cases:
int& ref(int& x) { return x; }
const int& ref(const int& x) { return x; }
class A {
int x;
int f() const;
auto test1() const -> decltype(this);
auto test2() const -> decltype(ref(x));
auto test3() const -> decltype(f());
};
auto A::test1() const -> decltype(this) {
return this;
}
auto A::test2() const -> decltype(ref(x)) {
return ref(x);
}
auto A::test3() const -> decltype(f()) {
return f();
}
This gives the following compiler errors in the C++0x mode of gcc 4.7.1:
- test1(): invalid use of 'this' at top level
- test2(): prototype for 'int& A::test2() const' does not match any in class
'A' (candidate is: const int& A::test2() const); additionally, 'int A::x' is
private
- test3(): cannot call member function 'int A::f() const' without object;
additionally, 'int A::f() const' is private
In summary, in the trailing return type of a const member function definition
outside of a class declaration, it seems:
1. I cannot explicitly reference 'this'
2. I can reference data members, but not private ones, and they are not const
3. I cannot invoke member functions
I believe all three function definitions should compile. Similarly, inline
definitions of the same member functions have no such problems:
class B {
int x;
int f() const;
auto test1() const -> decltype(this) { return this; }
auto test2() const -> decltype(ref(x)) { return ref(x); }
auto test3() const -> decltype(f()) { return f(); }
};
It seems that issue #2 is a regression compared to gcc 4.6, which seemed to
allow some access to data members. Consider test4():
template<typename X>
class C {
const X& x;
auto test4() const -> decltype(x);
};
template<typename X>
auto C<X>::test4() const -> decltype(x) {
return x;
}
This test compiles without problems under gcc 4.6.3. Whereas gcc 4.7.1 gives:
prototype for 'decltype (((C<X>*)0)->C<X>::x) C<X>::test4() const' does not
match any in class 'C<X>' (candidate is: decltype (((const
C<X>*)this)->C<X>::x) C<X>::test4() const)
