https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78457
Bug ID: 78457
Summary: attempt to instantiate unused template
Product: gcc
Version: 6.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: barry.revzin at gmail dot com
Target Milestone: ---
The following fails to compile on any version of gcc (or clang) I tried:
#include <iostream>
template <class... Ts> struct X;
template <class T> struct X<T> { };
template <class... Us> struct Y { X<Us...> x; };
template <class... Ts>
std::ostream& operator<<(std::ostream& os, Y<Ts...> const& ) {
os << std::endl;
return os;
}
int main()
{ }
with the error:
prog.cc: In instantiation of 'struct Y<>':
prog.cc:10:16: required from here
prog.cc:6:44: error: 'Y<Us>::x' has incomplete type
template <class... Us> struct Y { X<Us...> x; };
^
prog.cc:3:31: note: declaration of 'struct X<>'
template <class... Ts> struct X;
^
but no instance of Y is ever created, much less Y<> in operator<<. Moreover,
replacing std::endl with '\n' makes the code compile.
