diff options
| -rw-r--r-- | library/std/src/thread/local.rs | 22 |
1 files changed, 20 insertions, 2 deletions
diff --git a/library/std/src/thread/local.rs b/library/std/src/thread/local.rs index fa08fdc1653..3b7c31826b9 100644 --- a/library/std/src/thread/local.rs +++ b/library/std/src/thread/local.rs @@ -134,10 +134,28 @@ impl<T: 'static> fmt::Debug for LocalKey<T> { /// thread_local! { /// pub static FOO: RefCell<u32> = RefCell::new(1); /// -/// #[allow(unused)] /// static BAR: RefCell<f32> = RefCell::new(1.0); /// } -/// # fn main() {} +/// +/// FOO.with(|foo| assert_eq!(*foo.borrow(), 1)); +/// BAR.with(|bar| assert_eq!(*bar.borrow(), 1.0)); +/// ``` +/// +/// This macro supports a special `const {}` syntax that can be used +/// when the initialization expression can be evaluated as a constant. +/// This can enable a more efficient thread local implementation that +/// can avoid lazy initialization. For types that do not +/// [need to be dropped][crate::mem::needs_drop], this can enable an +/// even more efficient implementation that does not need to +/// track any additional state. +/// +/// ``` +/// use std::cell::Cell; +/// thread_local! { +/// pub static FOO: Cell<u32> = const { Cell::new(1) }; +/// } +/// +/// FOO.with(|foo| assert_eq!(foo.get(), 1)); /// ``` /// /// See [`LocalKey` documentation][`std::thread::LocalKey`] for more |