https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82222
Bug ID: 82222
Summary: wrong uninitialized reference in lambda capture in
fold expression
Product: gcc
Version: 7.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: benni.buch at gmail dot com
Target Milestone: ---
int main(){
int dummy = 0;
[](auto& d, auto ... args){
([](auto ...){}(([&d](){}, args)), ...);
}(dummy, 0, 0);
}
is a valid program, but:
$ g++ -std=c++17 -o main gcc-test.cpp
gcc-test.cpp: In instantiation of 'main()::<lambda(auto:1&, auto:2 ...)> [with
auto:1 = int; auto:2 = {int, int}]':
gcc-test.cpp:5:15: required from here
gcc-test.cpp:4:20: error: member 'main()::<lambda(auto:1&, auto:2 ...)> [with
auto:1 = int; auto:2 = {int, int}]::<lambda()>::<d capture>' is uninitialized
reference
([](auto ...){}(([&d](){}, args)), ...);
^
I found this while implementing an output function:
#include <iostream>
#include <tuple>
template < typename Arg, typename ... Args >
void comma_separated_output(
std::ostream& os,
Arg const& arg,
Args const& ... args
){
std::apply([&os](auto const& ... args)mutable{
(os << ... << args);
}, arg);
(std::apply([&os](auto const& ... args)mutable{
((os << ", ") << ... << args);
}, args), ...);
}
int main(){
comma_separated_output(std::cout,
std::make_tuple(), std::make_tuple(), std::make_tuple());
}
$ g++ -std=c++17 -o main gcc-test.cpp
gcc-test.cpp: In instantiation of 'void comma_separated_output(std::ostream&,
const Arg&, const Args& ...) [with Arg = std::tuple<>; Args = {std::tuple<>,
std::tuple<>}; std::ostream = std::basic_ostream<char>]':
gcc-test.cpp:20:64: required from here
gcc-test.cpp:13:17: error: member 'comma_separated_output(std::ostream&, const
Arg&, const Args& ...) [with Arg = std::tuple<>; Args = {std::tuple<>,
std::tuple<>}; std::ostream = std::basic_ostream<char>]::<lambda(const auto:2&
...)>::<os capture>' is uninitialized reference
(std::apply([&os](auto const& ... args)mutable{
^
Tested with:
$ g++ --version
g++ (GCC) 7.2.1 20170911
