1// Copyright 2016 lazy-static.rs Developers
2//
3// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
4// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
5// http://opensource.org/licenses/MIT>, at your option. This file may not be
6// copied, modified, or distributed except according to those terms.
7
8extern crate core;
9extern crate std;
10
11use self::std::prelude::v1::*;
12use self::std::cell::Cell;
13use self::std::hint::unreachable_unchecked;
14use self::std::sync::Once;
15#[allow(deprecated)]
16pub use self::std::sync::ONCE_INIT;
17
18// FIXME: Replace Option<T> with MaybeUninit<T> (stable since 1.36.0)
19pub struct Lazy<T: Sync>(Cell<Option<T>>, Once);
20
21impl<T: Sync> Lazy<T> {
22    #[allow(deprecated)]
23    pub const INIT: Self = Lazy(Cell::new(None), ONCE_INIT);
24
25    #[inline(always)]
26    pub fn get<F>(&'static self, f: F) -> &T
27    where
28        F: FnOnce() -> T,
29    {
30        self.1.call_once(|| {
31            self.0.set(Some(f()));
32        });
33
34        // `self.0` is guaranteed to be `Some` by this point
35        // The `Once` will catch and propagate panics
36        unsafe {
37            match *self.0.as_ptr() {
38                Some(ref x) => x,
39                None => {
40                    debug_assert!(false, "attempted to derefence an uninitialized lazy static. This is a bug");
41
42                    unreachable_unchecked()
43                },
44            }
45        }
46    }
47}
48
49unsafe impl<T: Sync> Sync for Lazy<T> {}
50
51#[macro_export]
52#[doc(hidden)]
53macro_rules! __lazy_static_create {
54    ($NAME:ident, $T:ty) => {
55        static $NAME: $crate::lazy::Lazy<$T> = $crate::lazy::Lazy::INIT;
56    };
57}
58