use std::marker::PhantomData;
use std::mem;
use std::sync::Arc;

pub trait Database: Send + Sync + 'static {
    fn snapshot(&self) -> Box<dyn Snapshot>;
}

trait Snapshot: 'static {
    fn foo(&self);
}

struct DB {}

struct DBSnapshot<'a> {
    _lifetime: PhantomData<&'a ()>,
}

impl DB {
    fn snapshot(&self) -> DBSnapshot {
        DBSnapshot {
            _lifetime: PhantomData,
        }
    }
}

struct DBWrapper {
    db: Arc<DB>,
}

impl Database for DBWrapper {
    fn snapshot(&self) -> Box<dyn Snapshot> {
        Box::new(DBWrapperSnapshot {
            snapshot: self.db.snapshot(),
            db: Arc::clone(&self.db),
        })
    }
}

struct DBWrapperSnapshot {
    snapshot: DBSnapshot<'static>,
    db: Arc<DB>,
}

impl Snapshot for DBWrapperSnapshot {
    fn foo(&self) {}
}