• Start Date: 2014-06-25
• RFC PR: rust-lang/rfcs#139
• Rust Issue: rust-lang/rust#10504

Summary

Remove the coercion from Box<T> to &T from the language.

Motivation

The coercion between Box<T> to &T is not replicable by user-defined smart pointers and has been found to be rarely used 1. We already removed the coercion between Box<T> and &mut T in RFC 33.

Detailed design

The coercion between Box<T> and &T should be removed.

Note that methods that take &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 &T may be convenient.

Alternatives

The impact of not doing this is that the coercion will remain.

Unresolved questions

None.