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Explain why TypeFoldable is a sub-trait of TypeVisitable.

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Nicholas Nethercote 2023-09-13 08:55:44 +10:00
parent 593373f17d
commit df98a74c32
1 changed files with 6 additions and 0 deletions
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6
compiler/rustc_type_ir/src/fold.rs
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@ -51,6 +51,12 @@ use crate::{visit::TypeVisitable, Interner};
/// ///
/// To implement this conveniently, use the derive macro located in /// To implement this conveniently, use the derive macro located in
/// `rustc_macros`. /// `rustc_macros`.
///
/// This trait is a sub-trait of `TypeVisitable`. This is because many
/// `TypeFolder` instances use the methods in `TypeVisitableExt` while folding,
/// which means in practice almost every foldable type needs to also be
/// visitable. (However, there are some types that are visitable without being
/// foldable.)
pub trait TypeFoldable<I: Interner>: TypeVisitable<I> { pub trait TypeFoldable<I: Interner>: TypeVisitable<I> {
/// The entry point for folding. To fold a value `t` with a folder `f` /// The entry point for folding. To fold a value `t` with a folder `f`
/// call: `t.try_fold_with(f)`. /// call: `t.try_fold_with(f)`.