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impl DispatchFromDyn for Cell and UnsafeCell After some fruitful discussion on [Internals](https://internals.rust-lang.org/t/impl-dispatchfromdyn-for-cell-2/16520) here's my first PR to rust-lang/rust 🎉 Please let me know if there's something I missed. This adds `DispatchFromDyn` impls for `Cell`, `UnsafeCell` and `SyncUnsafeCell`. An existing test is also expanded to test the `Cell` impl (which requires the `UnsafeCell` impl) The different `RefCell` types can not implement `DispatchFromDyn` since they have more than one (non ZST) field. **Edit:** ### What: These changes allow one to make types like `MyRc`(code below), to be object safe method receivers after implementing `DispatchFromDyn` and `Deref` for them. This allows for code like this: ```rust struct MyRc<T: ?Sized>(Cell<NonNull<RcBox<T>>>); /* impls for DispatchFromDyn, CoerceUnsized and Deref for MyRc*/ trait Trait { fn foo(self: MyRc<Self>); } let impls_trait = ...; let rc = MyRc::new(impls_trait) as MyRc<dyn Trait>; rc.foo(); ``` Note: `Cell` and `UnsafeCell` won't directly become valid method receivers since they don't implement `Deref`. Making use of these changes requires a wrapper type and nightly features. ### Why: A custom pointer type with interior mutability allows one to store extra information in the pointer itself. These changes allow for such a type to be a method receiver. ### Examples: My use case is a cycle aware custom `Rc` implementation that when dropping a cycle marks some references dangling. On the [forum](https://internals.rust-lang.org/t/impl-dispatchfromdyn-for-cell/14762/8) andersk mentioned that they track if a `Gc` reference is rooted with an extra bit in the reference itself. |
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| .. | ||
| auxiliary | ||
| elision | ||
| arbitrary_self_types_nested.rs | ||
| arbitrary_self_types_pin_lifetime_impl_trait-async.rs | ||
| arbitrary_self_types_pin_lifetime_impl_trait-async.stderr | ||
| arbitrary_self_types_pin_lifetime_impl_trait.rs | ||
| arbitrary_self_types_pin_lifetime_impl_trait.stderr | ||
| arbitrary_self_types_pin_lifetime_mismatch-async.rs | ||
| arbitrary_self_types_pin_lifetime_mismatch-async.stderr | ||
| arbitrary_self_types_pin_lifetime_mismatch.rs | ||
| arbitrary_self_types_pin_lifetime_mismatch.stderr | ||
| arbitrary_self_types_pin_lifetime-async.rs | ||
| arbitrary_self_types_pin_lifetime.rs | ||
| arbitrary_self_types_pointers_and_wrappers.rs | ||
| arbitrary_self_types_raw_pointer_struct.rs | ||
| arbitrary_self_types_raw_pointer_trait.rs | ||
| arbitrary_self_types_silly.rs | ||
| arbitrary_self_types_stdlib_pointers.rs | ||
| arbitrary_self_types_struct.rs | ||
| arbitrary_self_types_trait.rs | ||
| arbitrary_self_types_unsized_struct.rs | ||
| arbitrary-self-types-not-object-safe.curr.stderr | ||
| arbitrary-self-types-not-object-safe.object_safe_for_dispatch.stderr | ||
| arbitrary-self-types-not-object-safe.rs | ||
| builtin-superkinds-self-type.rs | ||
| by-value-self-in-mut-slot.rs | ||
| class-missing-self.rs | ||
| class-missing-self.stderr | ||
| explicit_self_xcrate_exe.rs | ||
| explicit-self-closures.rs | ||
| explicit-self-generic.rs | ||
| explicit-self-objects-uniq.rs | ||
| explicit-self.rs | ||
| issue-61882-2.rs | ||
| issue-61882-2.stderr | ||
| issue-61882.rs | ||
| issue-61882.stderr | ||
| move-self.rs | ||
| object-safety-sized-self-by-value-self.rs | ||
| object-safety-sized-self-generic-method.rs | ||
| object-safety-sized-self-return-Self.rs | ||
| objects-owned-object-owned-method.rs | ||
| point-at-arbitrary-self-type-method.rs | ||
| point-at-arbitrary-self-type-method.stderr | ||
| point-at-arbitrary-self-type-trait-method.rs | ||
| point-at-arbitrary-self-type-trait-method.stderr | ||
| self_lifetime-async.rs | ||
| self_lifetime.rs | ||
| self_type_keyword-2.rs | ||
| self_type_keyword-2.stderr | ||
| self_type_keyword.rs | ||
| self_type_keyword.stderr | ||
| self-impl-2.rs | ||
| self-impl.rs | ||
| self-impl.stderr | ||
| self-in-mut-slot-default-method.rs | ||
| self-in-mut-slot-immediate-value.rs | ||
| self-in-typedefs.rs | ||
| self-infer.rs | ||
| self-infer.stderr | ||
| self-re-assign.rs | ||
| self-shadowing-import.rs | ||
| self-type-param.rs | ||
| self-vs-path-ambiguity.rs | ||
| self-vs-path-ambiguity.stderr | ||
| string-self-append.rs | ||
| suggest-self-2.rs | ||
| suggest-self-2.stderr | ||
| suggest-self.rs | ||
| suggest-self.stderr | ||
| ufcs-explicit-self.rs | ||
| uniq-self-in-mut-slot.rs | ||
| where-for-self.rs | ||