Takes each element in the Iterator: if it is None, no further elements are taken, and the None is returned. Should no None occur, a vector containing the values of each Option is returned.

Here is an example which increments every integer in a vector, checking for overflow:

fn inc_conditionally(x: uint) -> Option<uint> {
    if x == uint::MAX { return None; }
    else { return Some(x+1u); }
}
let v = [1u, 2, 3];
let res = collect(v.iter().map(|&x| inc_conditionally(x)));
assert!(res == Some(~[2u, 3, 4]));