Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

requirements for const-eval #2

Merged
merged 1 commit into from
Jan 6, 2022
Merged

requirements for const-eval #2

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
14 changes: 14 additions & 0 deletions design-docs/const-eval-requirements.md
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,14 @@
# Const eval requirements

For this to work, const operations have to be deterministic and
must not depend on any external state,
at least when they are used in the type system.

Using floats during CTFE is fully determinstic. So using
them inside of the type system is fine. CTFE can however
produce different results than what would happen on real hardware,
but this is not a concern for const generics.

Other sources of non-determinism are allocations. This non-determinism
must however not be observed during const-evaluation (TODO: link to const-eval).
Any references used in a constant are considered equal if their targets are equal, which is also determistic. (ref [val-trees](https://github.com/rust-lang/rust/issues/72396))