Derive Copy and Clone HeaderSlice and HeaderWithLength #92
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We (apollo-compiler) have an AST where most nodes are wrapped in, approximately: ```rust struct Node<T>(triomphe::Arc<(SourceSpan, T)>); ``` `Arc` allows subtrees to be shared without deep cloning, and `Arc::make_mut` is used extensively for mutability with clone-on-write semantics. Now I would like to also support `Node<str>` and rely on `Arc::from_header_and_str` for the unsafe bits. This requires using `HeaderSlice` which with triomphe v0.1.12 breaks `Arc::make_mut` because it does not implement `Clone`. This PR fixes that. `Clone` cannot work for `T: !Sized` which is the main use case for `HeaderSlice` but that’s ok, `derive` automatically insert the appropriate `where` bound. This is still useful in order to have the same `Node<T>` use `HeaderSlice` to support both `T: Sized` and `T: !Sized`. (The names of `HeaderSlice` and its `slice` field are weird when `T: Sized` but that weirdness is contained in the module defining `struct Node`.) While I don’t have a use for this today this PR also derives `Copy`, and gives `HeaderWithLength` the same treatment.
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If you’re happy with this change, it’d be helpful to also have it on crates.io. Thanks! |
Manishearth
approved these changes
Jun 17, 2024
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We (apollo-compiler) have an AST where most nodes are wrapped in, approximately:
Arcallows subtrees to be shared without deep cloning, andArc::make_mutis used extensively for mutability with clone-on-write semantics.Now I would like to also support
Node<str>and rely onArc::from_header_and_strfor the unsafe bits. This requires usingHeaderSlicewhich with triomphe v0.1.12 breaksArc::make_mutbecause it does not implementClone. This PR fixes that.Clonecannot work forT: !Sizedwhich is the main use case forHeaderSlicebut that’s ok,deriveautomatically insert the appropriatewherebound. This is still useful in order to have the sameNode<T>useHeaderSliceto support bothT: SizedandT: !Sized. (The names ofHeaderSliceand itsslicefield are weird whenT: Sizedbut that weirdness is contained in the module definingstruct Node.)While I don’t have a use for this today this PR also derives
Copy, and givesHeaderWithLengththe same treatment.