Provides a Send-able cell type whose contents can be accessed only via an
inforgeable token.
```rust let mut token = Token::new();
let lock = TokenLock::new(&token, 1); assert_eq!(*lock.read(&token).unwrap(), 1);
let mut guard = lock.write(&mut token).unwrap(); assert_eq!(*guard, 1); *guard = 2; ```
TokenLock implements Send and Sync so it can be shared between threads,
but only the thread holding the original Token can access its contents.
Token cannot be cloned:
```rust let lock = Arc::new(TokenLock::new(&token, 1));
let lock1 = Arc::clone(&lock); thread::Builder::new().spawn(move || { let lock1 = lock1; let mut token1 = token;
// I have `Token` so I can get a mutable reference to the contents
lock_1.write(&mut token_1).unwrap();
}).unwrap();
// can't access the contents; I no longer have Token
// lock.write(&mut token).unwrap();
```
The lifetime of the returned reference is limited by both of the TokenLock
and Token.
rust
let mut token = Token::new();
let lock = TokenLock::new(&token, 1);
let guard = lock.write(&mut token).unwrap();
drop(lock); // compile error: `guard` cannot outlive `TokenLock`
rust
drop(token); // compile error: `guard` cannot outlive `Token`
It also prevents from forming a reference to the contained value when there already is a mutable reference to it:
rust
let write_guard = lock.write(&mut token).unwrap();
let read_guard = lock.read(&token).unwrap(); // compile error
While allowing multiple immutable references:
rust
let read_guard1 = lock.read(&token).unwrap();
let read_guard2 = lock.read(&token).unwrap();
License: MIT/Apache-2.0