lang (typesystem | references | coercions)
Remove the coercion from Box<T> to &mut T from the language.
Currently, the coercion between Box<T> to &mut T can be a hazard because it can lead to surprising mutation where it was not expected.
The coercion between Box<T> and &mut T should be removed.
Note that methods that take &mut self can still be called on values of type Box<T> without any special referencing or dereferencing. That is because the semantics of auto-deref and auto-ref conspire to make it work: the types unify after one autoderef followed by one autoref.
Borrowing from Box<T> to &mut T may be convenient.
An alternative is to remove &T coercions as well, but this was decided against as they are convenient.
The impact of not doing this is that the coercion will remain.
None.