In my experience, it is absolutely vital for performance to have both "owning" and "slice"/"view" string types, as well as sensible conversions between them. T

In my experience, it is absolutely vital for performance to have both "owning" and "slice"/"view" string types, as well as sensible conversions between them. This is actually an area where the C++ standard library has been lacking until recently. For example, you'd typically want a map with string keys to own them, but without severe contortions that meant map readers had to allocate a string key (expensive!) to perform a lookup.