X-Git-Url: https://git.ralfj.de/web.git/blobdiff_plain/b01ea6eb37bd201791375ac95bad460ba8081168..3acdc3ddcbcb0fc36eb2eff816663fddbdc471a6:/personal/_posts/2017-07-17-types-as-contracts.md diff --git a/personal/_posts/2017-07-17-types-as-contracts.md b/personal/_posts/2017-07-17-types-as-contracts.md index 10a8e4c..3ef565a 100644 --- a/personal/_posts/2017-07-17-types-as-contracts.md +++ b/personal/_posts/2017-07-17-types-as-contracts.md @@ -320,7 +320,7 @@ One topic that needs special treatment in this context is interior mutability. If a function takes an `x: &Cell`, following the rules above, it will acquire a read lock of `*x` for the duration of the function call, making `*x` immutable. Clearly, we do not want to do that -- calling `x.set` *will* actually mutate `*x`, and mutating through a shared reference is exactly the point of using `Cell`! -Lucky enough, the compiler *already* says that interior mutability is only allowed via [`UnsafeCell`](https://doc.rust-lang.org/beta/core/cell/struct.UnsafeCell.html). +Lucky enough, the compiler *already* says that interior mutability is only allowed via [`UnsafeCell`](https://doc.rust-lang.org/stable/core/cell/struct.UnsafeCell.html). We can use this for our purposes: To adjust validation for interior mutability, we *stop* our recursive descent and do not do anything when reaching an `UnsafeCell` *while `mutbl` indicates we are in immutable mode* -- `&mut UnsafeCell` is not affected. In particular, no locks are acquired. This justifies calling `set` on a shared reference and having the value changed.