Just like with accepting special values to signify the no value of a parameter, a function can sometimes return no value. Which of the following would you prefer?
int try_parse(std::string_view maybe_number);
bool try_parse(std::string_view maybe_number, int &parsed_number);
int *try_parse(std::string_view maybe_number);
std::optional<int> try_parse(std::string_view maybe_number);
How can you tell what value the first function will return in case of errors? Or will it throw an exception instead of returning a magic value? Moving on to the second signature, it looks like false will be returned if there is an error, but it's still easy to just forget to check it and read parsed_number directly, potentially causing trouble. In the third case, while it's relatively safe to assume a nullptr will be returned on errors and an integer in case of success, it's now unclear if the returned int should be freed.
With the last signature...