The code below compiles fine with gcc 3.3.1 and 3.4.0 (and does the right
thing); it produces a compile time error in 4.0.2. Lookup of the << operator
in the definition of serializable::impl<X>::value fails when it is instatiated
via the bar or baz templates but succeeds when instantiated via the foo
template. (Use of the bar or baz templates will succeed if instantation has
alread occured.)
Curiously, the bug seems very specific -- a number of very similar pieces of
code in 4.0.2's <tr1/type_traits> header compile correctly.
// --------------------
extern "C" int printf( char const*, ... );
namespace std2 {
class ostream { void* ptr; };
class string;
ostream& operator<<( ostream&, string const& );
}
namespace serializable {
struct two { std2::ostream a, b; };
template <class U, class V> two operator<<(U&, V const&);
template <class T>
struct impl {
static T const& make();
static std2::ostream& stream();
static const bool value
= sizeof( stream() << make() ) == sizeof(std2::ostream);
};
}
template <bool V> struct foo { foo() { printf("%d\n", V); } };
template <typename T> struct baz : foo< T::value > {};
template <typename T> struct bar : baz< serializable::impl<T> > {};
struct X {};
int main() {
bar< X >(); // -- Fails
baz< serializable::impl<X> >(); // -- Fails
foo< serializable::impl<X>::value >(); // -- Succeeds
baz< serializable::impl<X> >(); // -- Succeeds
bar< X >(); // -- Succeeds
}
// Expected output: 0 0 0 0 0
--
Summary: Bug in name lookup in template -- 4.0 regression against
3.4
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: richard at ex-parrot dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25153
