- Start Date: 2014-06-09
- RFC PR: rust-lang/rfcs#112
- Rust Issue: rust-lang/rust#10504
Summary
Remove the coercion from Box<T>
to &mut T
from the language.
Motivation
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.
Detailed design
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.
Drawbacks
Borrowing from Box<T>
to &mut T
may be convenient.
Alternatives
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.
Unresolved questions
None.