mirror
/
rustc-dev-guide
mirror of https://github.com/rust-lang/rustc-dev-guide.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

mention `WithOptConstParam` (#1346)

This commit is contained in:
lcnr 2022-05-09 02:19:43 +02:00 committed by GitHub
parent f76f69f603
commit b7b14a983a
1 changed files with 8 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
src/constants.md
View File

@ -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