https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66092
Bug ID: 66092
Summary: Concept can't check variadic template arguments
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: yingpo.liao at gmail dot com
Target Milestone: ---
Concept can't check variadic template arguments (r222891).
The example code shows an implementation of a concept to check if all types are
the same via variadic template arguments. It will be okay if we directly print
out the results, but will fail (internal compiler error) if we apply the
concept to real cases, i.e., a foo() function.
$ svn info
Path: .
Working Copy Root Path:
/Users/liao/Downloads/gcc-branch-c++-concepts/c++-concepts
URL: svn://gcc.gnu.org/svn/gcc/branches/c++-concepts
Relative URL: ^/branches/c++-concepts
Repository Root: svn://gcc.gnu.org/svn/gcc
Repository UUID: 138bc75d-0d04-0410-961f-82ee72b054a4
Revision: 222891
Node Kind: directory
Schedule: normal
Last Changed Author: asutton
Last Changed Rev: 222891
Last Changed Date: 2015-05-07 15:25:15 -0500 (Thu, 07 May 2015)
$ cat test.cpp
#include <iostream>
#include <type_traits>
template <typename T, typename U, typename... Args>
requires (sizeof...(Args) == 0)
constexpr decltype(auto) check()
{
return std::integral_constant<bool, __is_same_as(T, U)>();
}
template <typename T, typename U, typename... Args>
requires (sizeof...(Args) > 0)
constexpr decltype(auto) check()
{
return std::integral_constant<bool, __is_same_as(T, U)
&& decltype(check<U, Args...>())::value>();
}
template <typename T, typename U, typename... Args>
concept bool Same()
{
return decltype(check<T, U, Args...>())::value;
}
template <typename... Args>
requires Same<Args...>()
void foo( Args... args ) {}
int main()
{
// OK: print "true"
std::cout << std::boolalpha << Same<int, int, int>() << std::endl;
// ERROR
foo(1, 2, 3);
return 0;
}
$ g++ -std=c++1z test.cpp -o test
test.cpp:22:41: internal compiler error: tree check: accessed elt 2 of tree_vec
with 1 elts in tsubst, at cp/pt.c:12556
return decltype(check<T, U, Args...>())::value;
^
test.cpp:22:41: internal compiler error: Abort trap: 6
g++: internal compiler error: Abort trap: 6 (program cc1plus)
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.
