pub fn replace<T>(dest: &mut T, src: T) -> T
Replace the value at a mutable location with a new one, returning the old value, without deinitialising or copying either one.
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).