"Of course there are other concerns in doing this, such as testing, maintenance, etc but from a performance point of view the idea that "you couldn't write a be

"Of course there are other concerns in doing this, such as testing, maintenance, etc but from a performance point of view the idea that "you couldn't write a better version than the expert's implementation in the standard library" is not really true." Perhaps, but the bigger problem is that usually in order to know you've written the better version, you need to have actually used the library in a use case as close to the real one as possible and MEASURED.