- Start Date: 2014-06-09
- RFC PR: rust-lang/rfcs#111
- Rust Issue: rust-lang/rust#6515
Summary
Index
should be split into Index
and IndexMut
.
Motivation
Currently, the Index
trait is not suitable for most array indexing tasks. The slice functionality cannot be replicated using it, and as a result the new Vec
has to use .get()
and .get_mut()
methods.
Additionally, this simply follows the Deref
/DerefMut
split that has been implemented for a while.
Detailed design
We split Index
into two traits (borrowed from @nikomatsakis):
// self[element] -- if used as rvalue, implicitly a deref of the result
trait Index<E,R> {
fn index<'a>(&'a self, element: &E) -> &'a R;
}
// &mut self[element] -- when used as a mutable lvalue
trait IndexMut<E,R> {
fn index_mut<'a>(&'a mut self, element: &E) -> &'a mut R;
}
Drawbacks
-
The number of lang. items increases.
-
This design doesn’t support moving out of a vector-like object. This can be added backwards compatibly.
-
This design doesn’t support hash tables because there is no assignment operator. This can be added backwards compatibly.
Alternatives
The impact of not doing this is that the []
notation will not be available to Vec
.
Unresolved questions
None that I’m aware of.