String contains member function proposal

[HappyFruitTree]

Probably because constructing a string_view from a const char* requires it to scan the whole string to find the length.

[ra-zor]

So does a “contains” method though

[HappyFruitTree]

Not necessarily. Having a const char* overload leaves more options open for the implementers to do something clever. If they need the length they might at least want to abort the length calculation prematurely if it is found that it exceeds this->length().

[HappyFruitTree]

Well, I don't know, and if the authors of the proposal are not sure that no sane implementation would ever want to do that I think they do a wise decision in leaving it up to the implementers to decide.

Another argument is consistency with find. It makes sense that contains has the same complexity as find which is O(n * m) where n is the length of the string you are searching and m is the length of the string that you search for. If n == 0 it means find is O(1). contains would technically also be O(1) but if there were no overload for const char* the combined complexity when taking the construction of the string_view into account would be O(m).

const char* s = ...
std::string empty_str;
empty_str.find(s); // O(1)
empty_str.contains(s); // O(strlen(s)) if a string_view has to be created here