trait WorkspaceLog {
    fn get(&self) -> usize;
}

struct TheLog<'a>(&'a FilesystemOverlay);

impl<'a> WorkspaceLog for TheLog<'a> {
    fn get(&self) -> usize {
        (self.0).0
    }
}

trait WorkspaceController<'a> {
    type Log: WorkspaceLog;
    fn get_log(&'a self) -> Self::Log;
}

struct FilesystemOverlay(usize);

struct FSWorkspaceController<'a>(&'a mut FilesystemOverlay);

impl<'a> WorkspaceController<'a> for FSWorkspaceController<'a> {
    type Log = TheLog<'a>;

    fn get_log(&'a self) -> Self::Log {
        TheLog(&*self.0)
    }
}

trait AsWorkspaceController<'a> {
    type Controller: WorkspaceController<'a>;

    fn get_controller(self) -> Self::Controller;
}

impl<'a> AsWorkspaceController<'a> for &'a mut FilesystemOverlay {
    type Controller = FSWorkspaceController<'a>;

    fn get_controller(self) -> FSWorkspaceController<'a> {
        FSWorkspaceController(self)
    }
}

fn init1(control_dir: &mut FilesystemOverlay) -> usize {
    let controller = control_dir.get_controller();
    let log = controller.get_log();
    log.get()
}

fn init2<'a, O>(control_dir: O) -> usize
    where O: AsWorkspaceController<'a> {
    let controller = control_dir.get_controller();
    let log = controller.get_log();
    log.get()
}

fn main() {
    let mut control_dir = FilesystemOverlay(5);
    dbg!(init1(&mut control_dir));
    dbg!(init2(&mut control_dir));
}