| Summary: | [4.9/5 Regression] Error in template instantiation in GCC 4.9, works fine in GCC 4.8 | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Freddie Chopin <freddie.chopin> |
| Component: | c++ | Assignee: | Jason Merrill <jason> |
| Status: | RESOLVED FIXED | ||
| Severity: | normal | CC: | jason, ville.voutilainen |
| Priority: | P3 | Keywords: | rejects-valid |
| Version: | 4.9.2 | ||
| Target Milestone: | 4.9.3 | ||
| Host: | Target: | ||
| Build: | Known to work: | 4.8.2 | |
| Known to fail: | 4.9.1, 5.0 | Last reconfirmed: | 2015-01-12 00:00:00 |
The question at stackoverflow has an answer with much simpler test-case which also shows the problem. http://stackoverflow.com/a/27810002/157344 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- template<typename... T> struct Functor { template <T...> struct Inner {}; }; template struct Functor<>::Inner<>; int main() { } --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- Compiled with GCC 4.9.2: --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- $ g++ -std=c++11 test.cpp test.cpp: In instantiation of ‘struct Functor<>’: test.cpp:9:26: required from here test.cpp:5:12: error: wrong number of template arguments (1, should be 0) struct Inner ^ test.cpp:5:12: error: provided for ‘template<class ... T> template<T ...<anonymous> > struct Functor<T>::Inner’ test.cpp:5:12: error: wrong number of template arguments (1, should be 0) test.cpp:5:12: error: provided for ‘template<class ... T> template<T ...<anonymous> > struct Functor<T>::Inner’ test.cpp:9:28: error: ‘Inner’ is not a class template template struct Functor<>::Inner<>; ^ test.cpp:9:28: error: ‘Inner’ in ‘struct Functor<>’ does not name a type --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- Works fine with GCC 4.8. The answer also suggests there might be another similar bug, possibly related to the first one. Author: jason Date: Tue Jan 13 21:04:35 2015 New Revision: 219558 URL: https://gcc.gnu.org/viewcvs?rev=219558&root=gcc&view=rev Log: PR c++/64514 * pt.c (coerce_template_parameter_pack): Return NULL for a zero-length fixed parameter pack with a pack expansion arg. Added: trunk/gcc/testsuite/g++.dg/cpp0x/variadic165.C Modified: trunk/gcc/cp/ChangeLog trunk/gcc/cp/pt.c Author: jason Date: Wed Jan 28 17:21:06 2015 New Revision: 220210 URL: https://gcc.gnu.org/viewcvs?rev=220210&root=gcc&view=rev Log: PR c++/64514 * pt.c (coerce_template_parameter_pack): Return NULL for a zero-length fixed parameter pack with a pack expansion arg. Added: branches/gcc-4_9-branch/gcc/testsuite/g++.dg/cpp0x/variadic165.C Modified: branches/gcc-4_9-branch/gcc/cp/ChangeLog branches/gcc-4_9-branch/gcc/cp/pt.c Fixed for 4.9.3/5 |
The test code below works perfectly fine with GCC 4.8 (and 4.7): --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- #include <type_traits> template<typename T, T &object, typename... Args> struct Functor { template<float (T::*function)(Args...), Args... args> struct Inner { float operator()() const { return (object.*function)(args...); } }; }; class Object { public: float someFunction() { return {}; } float someFunctionWithArgument(int) { return {}; } }; Object object; Functor<Object, object>::Inner<&Object::someFunction> functor1; Functor<Object, object, int>::Inner<&Object::someFunctionWithArgument, 1> functor2; int main() { } --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- However with GCC 4.9 it fails with a rather unhelpful message at the point of instantiation of functor1: --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- $ g++ -std=c++11 test.cpp test.cpp: In instantiation of ‘struct Functor<Object, (* & object)>’: test.cpp:33:24: required from here test.cpp:7:9: error: wrong number of template arguments (2, should be 1) struct Inner ^ test.cpp:7:9: error: provided for ‘template<class T, T& object, class ... Args> template<float (T::* function)(Args ...), Args ...args> struct Functor<T, object, Args>::Inner’ test.cpp:7:9: error: wrong number of template arguments (2, should be 1) test.cpp:7:9: error: provided for ‘template<class T, T& object, class ... Args> template<float (T::* function)(Args ...), Args ...args> struct Functor<T, object, Args>::Inner’ test.cpp:33:26: error: ‘Inner’ in ‘struct Functor<Object, (* & object)>’ does not name a template type Functor<Object, object>::Inner<&Object::someFunction> functor1; ^ --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- >8 --- If I comment the line with functor1 instantiation, everything else (functor2) works fine. At the stackoverflow question I asked ( http://stackoverflow.com/questions/27802404/error-in-template-instantiation-in-gcc-4-9-works-fine-in-gcc-4-8?noredirect=1#comment44015634_27802404 ) it was reported that clang 3.5 and Visual Studio 2015 Preview accept this code, while intel 14 errors out (with an unreported message) and solaris studio 12.4 crashes. Is there something wrong with this code (which was working for me for over 2 years with older versions) or maybe this is a regression?