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mention WithOptConstParam #1346

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May 9, 2022
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mention WithOptConstParam #1346

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8 changes: 8 additions & 0 deletions src/constants.md
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Expand Up @@ -4,6 +4,14 @@ Constants used in the type system are represented as [`ty::Const`].
The variants of their [`ty::ConstKind`] mostly mirror the variants of [`ty::TyKind`]
with the two *additional* variants being `ConstKind::Value` and `ConstKind::Unevaluated`.

## `WithOptConstParam` and dealing with the query system

To typecheck constants used in the type system, we have to know their expected type.
For const arguments in type dependent paths, e.g. `x.foo::<{ 3 + 4 }>()`, we don't know
the expected type for `{ 3 + 4 }` until we are typechecking the containing function.

As we may however have to evaluate that constant during this typecheck, we would get a cycle error.
For more details, you can look at [this document](https://hackmd.io/@rust-const-generics/Bk5GHW-Iq).

## Unevaluated constants

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