https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71141
Bug ID: 71141
Summary: [concepts] Example variadic concept code in the
Concepts TS 14.1p9.4 rejected
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: tom at honermann dot net
CC: andrew.n.sutton at gmail dot com, asutton at gcc dot gnu.org
Target Milestone: ---
The following test case is taken from example code in the Concepts TS § 14.1
p9.4. gcc r236238 rejects this code. I presume the code is intended to be
well-formed; if not, then the Concepts TS should be updated.
$ cat t1.cpp
template<typename... Ts> concept bool C4 = true;
template<C4 T> void f5();
$ g++ -c -std=c++1z -fconcepts t1.cpp
t1.cpp:2:14: error: variadic constraint introduced without ‘...’ before ‘>’
token
template<C4 T> void f5();
^
The example is accepted if the constrained function is re-written with a
requires clause:
$ cat t2.cpp
template<typename... Ts> concept bool C4 = true;
template<typename T> requires C4<T> void f5();
$ g++ -c -std=c++1z -fconcepts t2.cpp; echo $?
0
An error is similarly produced when using a variadic non-type concept:
$ cat t3.cpp
template<char... Cs> concept bool C5 = true;
template<C5 C> void f7();
$ g++ -c -std=c++1z -fconcepts t3.cpp
t3.cpp:2:14: error: variadic constraint introduced without ‘...’ before ‘>’
token
template<C5 C> void f7();
^
