Associated types #1677
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Associated types #1677
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matklad
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Aug 11, 2019
| ast::PathSegmentKind::Angle { type_ref, trait_ref } => { | ||
| assert!(path.qualifier().is_none()); // this can only occur at the first segment | ||
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| // <T as Trait<A>>::Foo desugars to Trait<Self=T, A>::Foo |
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Let's add a TODO for <()>::default syntax.
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I kind of forgot about that syntax!
| @@ -91,6 +91,7 @@ impl ast::Attr { | |||
| #[derive(Debug, Clone, PartialEq, Eq)] | |||
| pub enum PathSegmentKind { | |||
| Name(ast::NameRef), | |||
| Angle { type_ref: Option<ast::TypeRef>, trait_ref: Option<ast::PathType> }, | |||
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Hm, should we perhaps introduce different variants for <Type> and <Type as Trait> flavors? I am also not too thrilled by Angle name, but UFCS is worse, and Qualified (used by "official" grammar) is outright confusing.
Perhaps just call it Type? That's what it is: <> is a way to explicitly switch from expr grammar to types grammar.
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Hmm yeah I'm fine with Type.
This adds three different representations, copied from the Chalk model: - `Ty::Projection` is an associated type projection written somewhere in the code, like `<Foo as Trait>::Bar`. - `Ty::UnselectedProjection` is similar, but we don't know the trait yet (`Foo::Bar`). - The above representations are normalized to their actual types during type inference. When that isn't possible, for example for `T::Item` inside an `fn foo<T: Iterator>`, the type is normalized to an application type with `TypeCtor::AssociatedType`.
I.e. `<T as Trait>::Foo`.
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1677: Associated types r=flodiebold a=flodiebold This implements basic support for (fully qualified) associated type projections: - handle fully qualified paths like `<T as Trait>::AssocType` (basically desugaring to something like `Trait<Self=T>::AssocType`) - lower these to a new `Ty::Projection` enum variant - also introduce `Ty::UnselectedProjection` for cases like `T::AssocType` where the trait from which the type comes isn't specified, but these aren't handled further so far - in inference, normalize these projections using Chalk: basically, when encountering a type e.g. from a type annotation or signature, we replace these `Ty::Projection`s by type variables and add obligations to normalize the associated type Co-authored-by: Florian Diebold <[email protected]>
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This implements basic support for (fully qualified) associated type projections:
<T as Trait>::AssocType(basically desugaring to something likeTrait<Self=T>::AssocType)Ty::Projectionenum variantTy::UnselectedProjectionfor cases likeT::AssocTypewhere the trait from which the type comes isn't specified, but these aren't handled further so farTy::Projections by type variables and add obligations to normalize the associated type