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 8 extern crate core; 9 extern crate std; 10 11 use self::std::prelude::v1::*; 12 use self::std::cell::Cell; 13 use self::std::hint::unreachable_unchecked; 14 use self::std::sync::Once; 15 #[allow(deprecated)] 16 pub use self::std::sync::ONCE_INIT; 17 18 // FIXME: Replace Option<T> with MaybeUninit<T> (stable since 1.36.0) 19 pub struct Lazy<T: Sync>(Cell<Option<T>>, Once); 20 21 impl<T: Sync> Lazy<T> { 22 #[allow(deprecated)] 23 pub const INIT: Self = Lazy(Cell::new(None), ONCE_INIT); 24 25 #[inline(always)] get<F>(&'static self, f: F) -> &T where F: FnOnce() -> T,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 49 unsafe impl<T: Sync> Sync for Lazy<T> {} 50 51 #[macro_export] 52 #[doc(hidden)] 53 macro_rules! __lazy_static_create { 54 ($NAME:ident, $T:ty) => { 55 static $NAME: $crate::lazy::Lazy<$T> = $crate::lazy::Lazy::INIT; 56 }; 57 } 58