Collect trait breaking changes
#107
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- Don't require `T: Sized` for `GcWeak::{from_ptr, cast}`
- Add `GcWeak::erase`
This gives a less footgunny way to trace `Gc<T>` pointers manually without accidentally dereferencing them and using `T`'s `Collect` impl instead (which is unsound!).
The following breaking changes are made: - Replaced `needs_trace()` by an associated constant `NEEDS_TRACE`. - The `Collection` type now takes a lifetime, and `Collect::trace` now takes a `Collection<'_>` instead of a `&Collection>`. - Added methods on `Collection<'_>` to trace values. - `Collect` is no longer object-safe. These changes allow the following optimizations: - Properly propagating `NEEDS_TRACE` in unsized types `RefLock<T>` and `[T]`. - Early bailout in `Collection::trace` if the value doesn't need to be traced, avoiding reliance on the optimizer to remove empty loops etc.
…cking To make this possible, moves the gray queues into a separate `MarkState` struct; also clean-up the big `do_collection_inner` loop by moving mark & sweep logic into their separate methods.
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Implements (mostly) the changes discussed in #105 (comment).
A small difference: I ditched the
CollectFlagsabstraction in favor of keeping a simple boolean; this makes the trait slightly less cumbersome to implement.This also refactors
Contextto drastically reduce the need forRefCelllocking, by borrowing the gray queues mutably during marking and tracing.