When would I pass const& std::string instead of std::string_view?

When would I choose std::string by const& instead of string_view for function arguments?

Do you need a null-terminated string? If so, then you should use std::string const& which gives you that guarantee. string_view does not – it’s simply a range of const char.

If you do not need a null-terminated string, and you do not need to take ownership of the data, then you should use string_view. If you do need to take ownership of the data, then it may be the case that string by value is better than string_view.