#include <string>
extern void use(int);
template<class... Ts>
void f(int i=1, Ts... ts)
{
use(sizeof...(Ts));
}
template<>
void f<std::string>(int i, std::string j)
{
use(j.size());
}
void test1()
{
f<std::string>();
}Godbolt
With -std=c++17 -O2 this compiles to std::abort().
I believe this should fail to compile due to none of the required parameters for the std::string specialization not being given.
