| Mellored |
It will trigger an attack of opportunity, but not many creatures have it.
Longbows have Volley 30', which gives -2 to hit anything within 30'.
They also just do less damage than a melee weapon, both as a smaller die, and they do not get Str to damage (half Str for some).
But there is no general rule. So if you want to sling a zombie, go ahead.