blob: 268dd45fd71fc0b7e980d94f0cb67f85c98b8790 [file] [log] [blame]
// Copyright 2016 Developers
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
//> or the MIT license <LICENSE-MIT or
//>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.
extern crate core;
extern crate std;
use self::std::prelude::v1::*;
use self::std::cell::Cell;
use self::std::sync::Once;
pub use self::std::sync::ONCE_INIT;
// FIXME: Replace Option<T> with MaybeInitialized<T>
pub struct Lazy<T: Sync>(Cell<Option<T>>, Once);
impl<T: Sync> Lazy<T> {
pub const INIT: Self = Lazy(Cell::new(None), ONCE_INIT);
pub fn get<F>(&'static self, f: F) -> &T
F: FnOnce() -> T,
self.1.call_once(|| {
// `self.0` is guaranteed to be `Some` by this point
// The `Once` will catch and propegate panics
unsafe {
match *self.0.as_ptr() {
Some(ref x) => x,
None => {
debug_assert!(false, "attempted to derefence an uninitialized lazy static. This is a bug");
unsafe impl<T: Sync> Sync for Lazy<T> {}
macro_rules! __lazy_static_create {
($NAME:ident, $T:ty) => {
static $NAME: $crate::lazy::Lazy<$T> = $crate::lazy::Lazy::INIT;
/// Polyfill for std::hint::unreachable_unchecked. There currently exists a
/// [crate]( for an equivalent to std::hint::unreachable_unchecked, but
/// lazy_static currently doesn't include any runtime dependencies and we've chosen to include this
/// short polyfill rather than include a new crate in every consumer's build.
/// This should be replaced by std's version when lazy_static starts to require at least Rust 1.27.
unsafe fn unreachable_unchecked() -> ! {
enum Void {}
match std::mem::uninitialized::<Void>() {}