template<typename... T>
auto foo(T&&... t){
    [](T&&... t){}(std::forward<T...>(t...)); // (1)

    return std::thread( // (2)
        [](T&&... t){},
        std::forward<T...>(t...)
    );
}

auto bar(){
    int n=1;
    foo(1); (A)
    foo(n); (B)
}