https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97819
Bug ID: 97819
Summary: Pack expansion in member initializer lists nested with
their parameter list got rejected.
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: gnaggnoyil at gmail dot com
Target Milestone: ---
The following code got accepted by Clang 10.0 and MSVC 19.27.29112, yet fails
to compile under GCC:
template <class ...Ts>
class foo : public Ts...{
public:
template <typename T, typename ...Us>
explicit foo(T &&t, Us &&...us)
//: Ts(Ts(t, us))...{} -> This line is accepted
//: Ts{t, us...}...{} -> This line is accepted too
: Ts(t, us...)...{} // This line is rejected
};
class bar{
public:
explicit bar(int){}
};
class qux{
public:
explicit qux(int){}
};
class baz{
public:
explicit baz(int){}
};
int main(){
foo<bar, baz, qux> x(3);
(void)x;
return 0;
}
I tried GCC version 4.9.3 with -std=c++14, 5.5.0, 6.3.0, 7.3.0 with -std=c++17,
and 8.3.0, 9.3.0, 10.1.0 with -std=c++2a, all of them rejects this code.
Error outputs for GCC 4.9.3, 5.5.0, 9.3.0, 10.1.0 ones are:
prog.cc: In instantiation of 'foo<Ts>::foo(T&&, Us&& ...) [with T = int; Us =
{}; Ts = bar, baz, qux]':
prog.cc:27:27: required from here
prog.cc:8:23: error: invalid use of pack expansion expression
: Ts(t, us...)...{}
^
Error outputs for GCC 6.3.0, 7.3.0, 8.3.0 ones are:
prog.cc: In instantiation of 'foo<Ts>::foo(T&&, Us&& ...) [with T = int; Us =
{}; Ts = {bar, baz, qux}]':
prog.cc:27:27: required from here
prog.cc:8:23: error: no matching function for call to 'bar::bar(int&, bool)'
: Ts(t, us...)...{}
^~~
prog.cc:13:14: note: candidate: bar::bar(int)
explicit bar(int){}
^~~
prog.cc:13:14: note: candidate expects 1 argument, 2 provided
prog.cc:11:7: note: candidate: constexpr bar::bar(const bar&)
class bar{
^~~
prog.cc:11:7: note: candidate expects 1 argument, 2 provided
prog.cc:11:7: note: candidate: constexpr bar::bar(bar&&)
prog.cc:11:7: note: candidate expects 1 argument, 2 provided
prog.cc:8:23: error: no matching function for call to 'baz::baz(int&, bool)'
: Ts(t, us...)...{}
^~~
prog.cc:23:14: note: candidate: baz::baz(int)
explicit baz(int){}
^~~
prog.cc:23:14: note: candidate expects 1 argument, 2 provided
prog.cc:21:7: note: candidate: constexpr baz::baz(const baz&)
class baz{
^~~
prog.cc:21:7: note: candidate expects 1 argument, 2 provided
prog.cc:21:7: note: candidate: constexpr baz::baz(baz&&)
prog.cc:21:7: note: candidate expects 1 argument, 2 provided
prog.cc:8:23: error: no matching function for call to 'qux::qux(int&, bool)'
: Ts(t, us...)...{}
^~~
prog.cc:18:14: note: candidate: qux::qux(int)
explicit qux(int){}
^~~
prog.cc:18:14: note: candidate expects 1 argument, 2 provided
prog.cc:16:7: note: candidate: constexpr qux::qux(const qux&)
class qux{
^~~
prog.cc:16:7: note: candidate expects 1 argument, 2 provided
prog.cc:16:7: note: candidate: constexpr qux::qux(qux&&)
prog.cc:16:7: note: candidate expects 1 argument, 2 provided
