| Summary: | C++0x parameter packs expansion problem | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Luca Mattiello <aiedail92> |
| Component: | c++ | Assignee: | Jason Merrill <jason> |
| Status: | RESOLVED FIXED | ||
| Severity: | normal | CC: | jason |
| Priority: | P3 | Keywords: | rejects-valid |
| Version: | 4.7.0 | ||
| Target Milestone: | 4.6.1 | ||
| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | 2011-04-04 18:16:41 | |
It certainly looks reasonable. Jason, should this be accepted? Yes, that's an obsolete restriction that has been removed from the draft; 8.3.5/13 used to say "A function parameter pack, if present, shall occur at the end of the parameter-declaration-list." but it doesn't any more. Jason, when this bug is fixed will this be allowed too?
template<typename... Args1>
struct S
{
template<typename... Args2>
void f(Args1... args1, Args2&&... args2)
{
}
};
S<int, int> s;
Currently this gives:
var.cc:5:47: error: parameter packs must be at the end of the parameter list
But it seems like it should be ok since sizeof...(Args1) is fixed when calling S::f and so shouldn't interfere with deducing Args2
(I wanted to do something of this form to make std::mem_fn support varargs member functions such as R (T::*)(int, ...) where Args1 would be [int] and Args2 would be the additional arguments passed to _Mem_fn::operator())
Yes, that looks OK too. Author: jason Date: Thu May 26 13:22:51 2011 New Revision: 174285 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=174285 Log: PR c++/48424 * decl.c (grokparms): Function parameter packs don't need to go at the end. * pt.c (type_unification_real): But they aren't deduced otherwise. Added: trunk/gcc/testsuite/g++.dg/cpp0x/variadic111.C Modified: trunk/gcc/cp/ChangeLog trunk/gcc/cp/decl.c trunk/gcc/cp/pt.c trunk/gcc/testsuite/ChangeLog trunk/gcc/testsuite/g++.dg/cpp0x/variadic41.C Fixed for 4.6.1. Author: jason Date: Thu May 26 13:44:20 2011 New Revision: 174287 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=174287 Log: PR c++/48424 * decl.c (grokparms): Function parameter packs don't need to go at the end. * pt.c (type_unification_real): But they aren't deduced otherwise. Added: branches/gcc-4_6-branch/gcc/testsuite/g++.dg/cpp0x/variadic111.C Modified: branches/gcc-4_6-branch/gcc/cp/ChangeLog branches/gcc-4_6-branch/gcc/cp/decl.c branches/gcc-4_6-branch/gcc/cp/pt.c branches/gcc-4_6-branch/gcc/testsuite/ChangeLog branches/gcc-4_6-branch/gcc/testsuite/g++.dg/cpp0x/variadic41.C |
The following testcase, which should be valid (at least I think so), fails to compile: #include <tuple> #include <functional> template<typename... T> struct test { std::tuple<int, T..., long> t; // OK void(*fptr)(int, T..., long); // Error (1) std::function<void(int, T..., long)> f; // Error (2) }; Since in (1) and (2) T... is not a parameter pack declaration, but a parameter pack expansion, shouldn't the code be valid? And if it's really not valid, is there a good explanation for this? luca@laptop-luca:~$ g++ --version g++ (GCC) 4.7.0 20110330 (experimental) luca@laptop-luca:~$ g++ -std=c++0x testcase.cc testcase.cc:8:32: error: parameter packs must be at the end of the parameter list testcase.cc:9:39: error: parameter packs must be at the end of the parameter list