# The Problem

We have a `CredentialManager` implementation which can be in two states: **locked** or **unlocked**.

When the manager is locked, it can be unlocked with the `unlock(...)` method. Now unlocked, the `set(...)` and `get(...)` methods can be performed on the manager. Also, it can be locked again using the `lock()` method.

```rust
let mut pw = CredentialManager::new();
pw.unlock("pssst");
pw.set("foo", "bar");
let val = pw.get("foo");
pw.lock();
```

But with the current implementation, on a locked manager, the `get` and `set` could be performed which would result in erroneous results.

```rust
let mut pw = CredentialManager::new();
pw.set("foo", "bar"); // -> 💥
```

Also, nothing prevents us from unlocking an already unlocked manager as well as locking an already locked manager.

```rust
let mut pw = CredentialManager::new();
pw.unlock("pssst");
pw.unlock("pssst"); // -> 💥

let mut pw = CredentialManager::new();
pw.lock(); // -> 💥
```