pub fn map_opt<T, U: ToStr, V>(o_t: &Option<T>, op: &fn(&T) -> Result<V, U>) -> Result<Option<V>, U>
Prefix searches with a type followed by a colon (e.g.
fn:) to restrict the search to a given type.
Accepted types are: fn, mod,
struct (or str), enum,
trait, typedef (or
tdef).