const generics update

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lcnr 2021-09-20 19:10:40 +02:00 committed by Joshua Nelson
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- [Generics and substitutions](./generics.md) - [Generics and substitutions](./generics.md)
- [`TypeFolder` and `TypeFoldable`](./ty-fold.md) - [`TypeFolder` and `TypeFoldable`](./ty-fold.md)
- [Generic arguments](./generic_arguments.md) - [Generic arguments](./generic_arguments.md)
- [Constants in the type system](./constants.md)
- [Type inference](./type-inference.md) - [Type inference](./type-inference.md)
- [Trait solving](./traits/resolution.md) - [Trait solving](./traits/resolution.md)
- [Early and Late Bound Parameters](./early-late-bound.md) - [Early and Late Bound Parameters](./early-late-bound.md)

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## Unevaluated constants ## Unevaluated constants
*This section talks about what's happening with `feature(const_generics)` enabled. *This section talks about what's happening with `feature(generic_const_exprs)` enabled.
On stable we do not yet supply any generic parameters to anonymous constants, On stable we do not yet supply any generic parameters to anonymous constants,
avoiding most of the issues mentioned here.* avoiding most of the issues mentioned here.*
Unless a constant is either a simple literal, e.g. `[u8; 3]` or `foo::<{ 'c' }>()`, Unless a constant is either a simple literal, e.g. `[u8; 3]` or `foo::<{ 'c' }>()`,
or a generic parameter, e.g. `[u8; N]`, converting a constant to its [`ty::Const`] representation or a generic parameter, e.g. `[u8; N]`, converting a constant to its [`ty::Const`] representation
returns an unevaluated constant. Even fully concrete constants which do not depend on a returns an unevaluated constant. Even fully concrete constants which do not depend on
generic parameter are not evaluated right away. generic parameters are not evaluated right away.
We do not eagerly evaluate constant as they can be used in the `where`-clauses of their We do not eagerly evaluate constant as they can be used in the `where`-clauses of their
parent item, for example: parent item, for example:
```rust ```rust
#[feature(const_generics, const_evaluatable_checked)] #[feature(generic_const_exprs)]
fn foo<T: Trait>() fn foo<T: Trait>()
where where
[u8; <T as Trait>::ASSOC + 1]: SomeOtherTrait, [u8; <T as Trait>::ASSOC + 1]: SomeOtherTrait,