# Parameterisation over mutability

**URL:** <https://internals.rust-lang.org/t/parameterisation-over-mutability/235>\
**Category:** ideas (deprecated)\
**Created:** [July 22, 2014, 7:50am UTC](https://internals.rust-lang.org/t/parameterisation-over-mutability/235 "2014-07-22T07:50:50Z")\
**Posts on this page:** 1\
**Showing post:** 3

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**Author:** ![huon](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/huon/32/3698_2.png) [@huon](https://internals.rust-lang.org/u/huon)\
**Post date:** [July 22, 2014, 9:37am UTC](https://internals.rust-lang.org/t/parameterisation-over-mutability/235/3 "2014-07-22T09:37:14Z")

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The `&const` Rust previously had doesn’t solve the problem, since you can’t use `fn find(&const self, key: uint) -> &const X` to get either a `&` out (if called on an `&` receiver) or a `&mut` (for a `&mut` receiver), you always get a `&const` out.

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