that's not my problem at all. i already implemented it.
the point i'm trying to make with this and several of my other postings: sfml is a really awesome library, but it's not perfect. i don't program that much with sfml these days since i already have to program at work, and it gets boring really fast. but even in the short time, i've come across small missing features on (too) many occasions. and those were clearly things that belong to the lib / engine. vector algebra is one of these things. if you have a vector class, you should make it right. it's not that hard, but i consider it ugly looking code when there are that many things that i needed to implement myself, just because programmer of the lib doesn't bother with such seemingly obsolete and trivial problems (no offense lauren, i appreciate your work).
but here's one of the many 1 hour work things that you could implement that would make your lib even more awesome. it's ok to discuss things like collision detection with sprites, since you want to keep your lib neutral , and cd is not a natural part of sprites themself. but thats not the case with vectors. you added them, and it's my personal suggestion that you should complete them. how can it hurt?
if you don't have the time or if you simply don't give a shit about this simply say it. you're not a business man and you can afford to simply say this. we will still love sfml and we will still appreciate your work
. just don't pass off every second suggestions by saying "implement it yourself"