[akling]

Because now you're holding a reference to `x` which is supposed to be protected by a mutex, even after the mutex is unlocked.

With the lambda-only API, it's much harder to make this mistake, since a temporary reference like this will still go out of scope at the end of the lambda expression.

[kajaktum]

You specifically mentioned that this is a footgun:

> auto& x = state.locked()->x;

But I don't see how the reference here is gonna make a difference unless i am reading the lifetime of the lock here incorrectly. For example, this is perfectly fine right?

```

{

auto& x = state.locked()->x;

}

```

This will only be a problem if you have an outside struct that holds a reference

```

auto &a = "something";

{

auto& x = state.locked()->x;

a = x;

}

```

Which can still happen even if you use a lambda.