    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    22
    23
    24
    25
    26
    27
    28
    29
    30
    31
    32
    33
    34
    35
    36
    37
    38
    39
    40
    41
    42
    43
    44
    45
    46
    47
    48
    49
    50
    51
    52
    53
    54
    55
    56
    57

    // Copyright 2016 lazy-static.rs Developers
    //
    // Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
    // http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
    // http://opensource.org/licenses/MIT>, 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::hint::unreachable_unchecked;
    use self::std::sync::Once;
    #[allow(deprecated)]
    pub use self::std::sync::ONCE_INIT;

    // FIXME: Replace Option<T> with MaybeUninit<T> (stable since 1.36.0)
    pub struct Lazy<T: Sync>(Cell<Option<T>>, Once);

    impl<T: Sync> Lazy<T> {
        #[allow(deprecated)]
        pub const INIT: Self = Lazy(Cell::new(None), ONCE_INIT);

        #[inline(always)]
        pub fn get<F>(&'static self, f: F) -> &T
        where
            F: FnOnce() -> T,
        {
            self.1.call_once(|| {
                self.0.set(Some(f()));
            });

            // `self.0` is guaranteed to be `Some` by this point
            // The `Once` will catch and propagate 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");

                        unreachable_unchecked()
                    },
                }
            }
        }
    }

    unsafe impl<T: Sync> Sync for Lazy<T> {}

    #[macro_export]
    #[doc(hidden)]
    macro_rules! __lazy_static_create {
        ($NAME:ident, $T:ty) => {
            static $NAME: $crate::lazy::Lazy<$T> = $crate::lazy::Lazy::INIT;
        };
    }