pub fn main(world: World) -> Void raises {
    let src: [5]u8 = [97, 103, 101, 110, 116]
    var dst: [5]u8 = [0, 0, 0, 0, 0]
    let copied: usize = std.mem.copy(dst, src)
    let copied_first: u8 = dst[0]
    let filled: usize = std.mem.fill(dst, 33_u8)
    if copied == 5 && copied_first == 97 as u8 && filled == 5 && dst[3] == 33_u8 {
        check world.out.write("mem copy fill ok\n")
    }
}