facet-rs / facet / 20024677191

58%

Build Type

push

github

Committed by fasterthanlime

Commit Message

feat: add variance-aware lifetime transformation methods to Peek

Add methods that allow safely transforming the 'facet lifetime parameter
based on the underlying type's variance:

- `variance()` - query the type's variance
- `shrink_lifetime()` - shrink lifetime for covariant types (panics otherwise)
- `try_shrink_lifetime()` - returns Option, None for non-covariant types
- `grow_lifetime()` - grow lifetime for contravariant types (panics otherwise)
- `try_grow_lifetime()` - returns Option, None for non-contravariant types

While Peek remains invariant by default (for soundness), these methods let
users opt-in to covariant/contravariant behavior when they know the
underlying type supports it, with runtime checks to ensure safety.

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