Struct OwnedRwLockMappedWriteGuard

use std::sync::Arc;
use tokio::sync::{RwLock, OwnedRwLockWriteGuard};

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
struct Foo(u32);

let lock = Arc::new(RwLock::new(Foo(1)));

{
    let lock = Arc::clone(&lock);
    let mut mapped = OwnedRwLockWriteGuard::map(lock.write_owned().await, |f| &mut f.0);
    *mapped = 2;
}

assert_eq!(Foo(2), *lock.read().await);

use std::sync::Arc;
use tokio::sync::{RwLock, OwnedRwLockWriteGuard};

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
struct Foo(u32);

let lock = Arc::new(RwLock::new(Foo(1)));

{
    let guard = Arc::clone(&lock).write_owned().await;
    let mut guard = OwnedRwLockWriteGuard::try_map(guard, |f| Some(&mut f.0)).expect("should not fail");
    *guard = 2;
}

assert_eq!(Foo(2), *lock.read().await);

use std::sync::Arc;
use tokio::sync::{
    RwLock,
    OwnedRwLockWriteGuard,
    OwnedRwLockMappedWriteGuard,
};

let lock = Arc::new(RwLock::new(1));

let guard = lock.clone().write_owned().await;
let guard = OwnedRwLockWriteGuard::map(guard, |x| x);
assert!(Arc::ptr_eq(&lock, OwnedRwLockMappedWriteGuard::rwlock(&guard)));