I think it might be trying to get at “dereferencing this does something special” (i.e. it’s not just a reference, but some type that manually implements Deref/D

I think it might be trying to get at “dereferencing this does something special” (i.e. it’s not just a reference, but some type that manually implements Deref/DerefMut). But it doesn’t actually do that—if you have a &mut String, .deref_mut() will give a &mut str (equivalent to &mut *self), but if you have a &mut str, .deref_mut() will give a &mut str too, by doing reference reborrowing (so the final result is equivalent to &mut **self). In the end, I’d prefer to deal with the sigils, because I think it’s a little easier to be confident what they’re going to do than calling the method that takes &mut self but effectively changes how it behaves depending on the type in question.