JoJoJet c43295af80 Simplify design for *Labels (#4957) ... # Objective - Closes #4954 - Reduce the complexity of the `{System, App, *}Label` APIs. ## Solution For the sake of brevity I will only refer to `SystemLabel`, but everything applies to all of the other label types as well. - Add `SystemLabelId`, a lightweight, `copy` struct. - Convert custom types into `SystemLabelId` using the trait `SystemLabel`. ## Changelog - String literals implement `SystemLabel` for now, but this should be changed with #4409 . ## Migration Guide - Any previous use of `Box<dyn SystemLabel>` should be replaced with `SystemLabelId`. - `AsSystemLabel` trait has been modified. - No more output generics. - Method `as_system_label` now returns `SystemLabelId`, removing an unnecessary level of indirection. - If you *need* a label that is determined at runtime, you can use `Box::leak`. Not recommended. ## Questions for later * Should we generate a `Debug` impl along with `#[derive(*Label)]`? * Should we rename `as_str()`? * Should we remove the extra derives (such as `Hash`) from builtin `*Label` types? * Should we automatically derive types like `Clone, Copy, PartialEq, Eq`? * More-ergonomic comparisons between `Label` and `LabelId`. * Move `Dyn{Eq, Hash,Clone}` somewhere else. * Some API to make interning dynamic labels easier. * Optimize string representation * Empty string for unit structs -- no debug info but faster comparisons * Don't show enum types -- same tradeoffs as asbove.		2022-07-14 18:23:01 +00:00
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src	Simplify design for *Labels (#4957)	2022-07-14 18:23:01 +00:00
Cargo.toml	Simplify design for *Labels (#4957)	2022-07-14 18:23:01 +00:00