Using the GNU extension for forward declaration of explicit instantiations
("extern template...") seems to make static member definitions fall under the
rules of declarations:
$ cat /tmp/t.cpp
struct C {};
template<typename T>
struct S { static T v; };
template<typename T>
T S<T>::v = T();
extern template class S<C>;
C c = S<C>::v;
$ bin/g++ -c /tmp/t.cpp
/tmp/t.cpp: In instantiation of C S<C>::v:
/tmp/t.cpp:11: instantiated from here
/tmp/t.cpp:7: error: S<C>::v cannot be initialized by a non-constant
expression when being declared
$ bin/g++ -v
Using built-in specs.
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc/configure --prefix=/M/src/inst --enable-languages=c++
--disable-bootstrap --disable-multilib
Thread model: posix
gcc version 4.3.0 20070810 (experimental)
Known workarounds for this issue are:
1. using g++ 3.x rather than the 4.1.3, 4.2.1 or trunk (r127350) that I tried
2. removing the "extern template" line
3. changing the order of the structure declaration, data member definition and
forward declaration lines
4. providing an explicit specialization of the static data members for the
forward-declared instantiations
--
Summary: "extern template" GNU extension makes static data member
definition a declaration
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: gcc-bugzilla at waba dot be
GCC build triplet: x86_64-linux-gnu
GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33047
