template <class T>
T foo(T a) {
 if (a) {
   // do somethin', returns object of type T
 } else {
   return NULL;
 }
}

template <class T>
T* foo(T a) {
 if (a) {
   // do somethin', returns object of type T*
 } else {
   return nullptr;
 }
}

template <class T>
std::optional<T> foo(T a) {
    if (a) {
        // do somethin', returns object of type T
        return std::make_optional(/*Anything that constructs `T`*/);
    } else {
        return {};
    }
}

auto my_val = foo(obj);
if(my_val){
     /* :-) ....knock yourself out! */
}
else{
     /* :-( ....we didn't find the value */
}

if(auto my_val = foo(obj); my_val){
     // ....knock yourself out!
}

return listData[i];

cout << "Does not exist";

return {};