# Changelog
## Unreleased
## 1.20.2
- Remove `portable_atomic` from Cargo.lock if it is not, in fact, used: [#267](https://github.com/matklad/once_cell/pull/267)
This is a work-around for this cargo bug: https://github.com/rust-lang/cargo/issues/10801.
## 1.20.1
- Allow using `race` module using just `portable_atomic`, without `critical_section` and provide
better error messages on targets without atomic CAS instruction,
[#265](https://github.com/matklad/once_cell/pull/265).
## 1.19.0
- Use `portable-atomic` instead of `atomic-polyfill`, [#251](https://github.com/matklad/once_cell/pull/251).
## 1.18.0
- `MSRV` is updated to 1.60.0 to take advantage of `dep:` syntax for cargo features,
removing "implementation details" from publicly visible surface.
## 1.17.2
- Avoid unnecessary synchronization in `Lazy::{force,deref}_mut()`, [#231](https://github.com/matklad/once_cell/pull/231).
## 1.17.1
- Make `OnceRef` implementation compliant with [strict provenance](https://github.com/rust-lang/rust/issues/95228).
## 1.17.0
- Add `race::OnceRef` for storing a `&'a T`.
## 1.16.0
- Add `no_std` implementation based on `critical-section`,
[#195](https://github.com/matklad/once_cell/pull/195).
- Deprecate `atomic-polyfill` feature (use the new `critical-section` instead)
## 1.15.0
- Increase minimal supported Rust version to 1.56.0.
- Implement `UnwindSafe` even if the `std` feature is disabled.
## 1.14.0
- Add extension to `unsync` and `sync` `Lazy` mut API:
- `force_mut`
- `get_mut`
## 1.13.1
- Make implementation compliant with [strict provenance](https://github.com/rust-lang/rust/issues/95228).
- Upgrade `atomic-polyfill` to `1.0`
## 1.13.0
- Add `Lazy::get`, similar to `OnceCell::get`.
## 1.12.1
- Remove incorrect `debug_assert`.
## 1.12.0
- Add `OnceCell::wait`, a blocking variant of `get`.
## 1.11.0
- Add `OnceCell::with_value` to create initialized `OnceCell` in `const` context.
- Improve `Clone` implementation for `OnceCell`.
- Rewrite `parking_lot` version on top of `parking_lot_core`, for even smaller cells!
## 1.10.0
- upgrade `parking_lot` to `0.12.0` (note that this bumps MSRV with `parking_lot` feature enabled to `1.49.0`).
## 1.9.0
- Added an `atomic-polyfill` optional dependency to compile `race` on platforms without atomics
## 1.8.0
- Add `try_insert` API -- a version of `set` that returns a reference.
## 1.7.2
- Improve code size when using parking_lot feature.
## 1.7.1
- Fix `race::OnceBox<T>` to also impl `Default` even if `T` doesn't impl `Default`.
## 1.7.0
- Hide the `race` module behind (default) `race` feature.
Turns out that adding `race` by default was a breaking change on some platforms without atomics.
In this release, we make the module opt-out.
Technically, this is a breaking change for those who use `race` with `no_default_features`.
Given that the `race` module itself only several days old, the breakage is deemed acceptable.
## 1.6.0
- Add `Lazy::into_value`
- Stabilize `once_cell::race` module for "first one wins" no_std-compatible initialization flavor.
- Migrate from deprecated `compare_and_swap` to `compare_exchange`.
## 1.5.2
- `OnceBox` API uses `Box<T>`.
This a breaking change to unstable API.
## 1.5.1
- MSRV is increased to `1.36.0`.
- document `once_cell::race` module.
- introduce `alloc` feature for `OnceBox`.
- fix `OnceBox::set`.
## 1.5.0
- add new `once_cell::race` module for "first one wins" no_std-compatible initialization flavor.
The API is provisional, subject to change and is gated by the `unstable` cargo feature.
## 1.4.1
- upgrade `parking_lot` to `0.11.0`
- make `sync::OnceCell<T>` pass https://doc.rust-lang.org/nomicon/dropck.html#an-escape-hatch[dropck] with `parking_lot` feature enabled.
This fixes a (minor) semver-incompatible changed introduced in `1.4.0`
## 1.4.0
- upgrade `parking_lot` to `0.10` (note that this bumps MSRV with `parking_lot` feature enabled to `1.36.0`).
- add `OnceCell::take`.
- upgrade crossbeam utils (private dependency) to `0.7`.
## 1.3.1
- remove unnecessary `F: fmt::Debug` bound from `impl fmt::Debug for Lazy<T, F>`.
## 1.3.0
- `Lazy<T>` now implements `DerefMut`.
- update implementation according to the latest changes in `std`.
## 1.2.0
- add `sync::OnceCell::get_unchecked`.
## 1.1.0
- implement `Default` for `Lazy`: it creates an empty `Lazy<T>` which is initialized with `T::default` on first access.
- add `OnceCell::get_mut`.
## 1.0.2
- actually add `#![no_std]` attribute if std feature is not enabled.
## 1.0.1
- fix unsoundness in `Lazy<T>` if the initializing function panics. Thanks [@xfix](https://github.com/xfix)!
- implement `RefUnwindSafe` for `Lazy`.
- share more code between `std` and `parking_lot` implementations.
- add F.A.Q section to the docs.
## 1.0.0
- remove `parking_lot` from the list of default features.
- add `std` default feature. Without `std`, only `unsync` module is supported.
- implement `Eq` for `OnceCell`.
- fix wrong `Sync` bound on `sync::Lazy`.
- run the whole test suite with miri.
## 0.2.7
- New implementation of `sync::OnceCell` if `parking_lot` feature is disabled.
It now employs a hand-rolled variant of `std::sync::Once`.
- `sync::OnceCell::get_or_try_init` works without `parking_lot` as well!
- document the effects of `parking_lot` feature: same performance but smaller types.
## 0.2.6
- Updated `Lazy`'s `Deref` impl to requires only `FnOnce` instead of `Fn`
## 0.2.5
- `Lazy` requires only `FnOnce` instead of `Fn`
## 0.2.4
- nicer `fmt::Debug` implementation
## 0.2.3
- update `parking_lot` to `0.9.0`
- fix stacked borrows violation in `unsync::OnceCell::get`
- implement `Clone` for `sync::OnceCell<T> where T: Clone`
## 0.2.2
- add `OnceCell::into_inner` which consumes a cell and returns an option
## 0.2.1
- implement `sync::OnceCell::get_or_try_init` if `parking_lot` feature is enabled
- switch internal `unsafe` implementation of `sync::OnceCell` from `Once` to `Mutex`
- `sync::OnceCell::get_or_init` is twice as fast if cell is already initialized
- implement `std::panic::RefUnwindSafe` and `std::panic::UnwindSafe` for `OnceCell`
- better document behavior around panics
## 0.2.0
- MSRV is now 1.31.1
- `Lazy::new` and `OnceCell::new` are now const-fns
- `unsync_lazy` and `sync_lazy` macros are removed
## 0.1.8
- update crossbeam-utils to 0.6
- enable bors-ng
## 0.1.7
- cells implement `PartialEq` and `From`
- MSRV is down to 1.24.1
- update `parking_lot` to `0.7.1`
## 0.1.6
- `unsync::OnceCell<T>` is `Clone` if `T` is `Clone`.
## 0.1.5
- No changelog until this point :(