use core::{ cell::Cell, sync::atomic::{AtomicUsize, Ordering::SeqCst}, }; use once_cell::unsync::OnceCell; #[test] fn once_cell() { let c = OnceCell::new(); assert!(c.get().is_none()); c.get_or_init(|| 92); assert_eq!(c.get(), Some(&92)); c.get_or_init(|| panic!("Kabom!")); assert_eq!(c.get(), Some(&92)); } #[test] fn once_cell_with_value() { const CELL: OnceCell = OnceCell::with_value(12); let cell = CELL; assert_eq!(cell.get(), Some(&12)); } #[test] fn once_cell_get_mut() { let mut c = OnceCell::new(); assert!(c.get_mut().is_none()); c.set(90).unwrap(); *c.get_mut().unwrap() += 2; assert_eq!(c.get_mut(), Some(&mut 92)); } #[test] fn once_cell_drop() { static DROP_CNT: AtomicUsize = AtomicUsize::new(0); struct Dropper; impl Drop for Dropper { fn drop(&mut self) { DROP_CNT.fetch_add(1, SeqCst); } } let x = OnceCell::new(); x.get_or_init(|| Dropper); assert_eq!(DROP_CNT.load(SeqCst), 0); drop(x); assert_eq!(DROP_CNT.load(SeqCst), 1); } #[test] fn once_cell_drop_empty() { let x = OnceCell::::new(); drop(x); } #[test] fn clone() { let s = OnceCell::new(); let c = s.clone(); assert!(c.get().is_none()); s.set("hello".to_string()).unwrap(); let c = s.clone(); assert_eq!(c.get().map(String::as_str), Some("hello")); } #[test] fn get_or_try_init() { let cell: OnceCell = OnceCell::new(); assert!(cell.get().is_none()); let res = std::panic::catch_unwind(|| cell.get_or_try_init(|| -> Result<_, ()> { panic!() })); assert!(res.is_err()); assert!(cell.get().is_none()); assert_eq!(cell.get_or_try_init(|| Err(())), Err(())); assert_eq!(cell.get_or_try_init(|| Ok::<_, ()>("hello".to_string())), Ok(&"hello".to_string())); assert_eq!(cell.get(), Some(&"hello".to_string())); } #[test] fn from_impl() { assert_eq!(OnceCell::from("value").get(), Some(&"value")); assert_ne!(OnceCell::from("foo").get(), Some(&"bar")); } #[test] fn partialeq_impl() { assert!(OnceCell::from("value") == OnceCell::from("value")); assert!(OnceCell::from("foo") != OnceCell::from("bar")); assert!(OnceCell::::new() == OnceCell::new()); assert!(OnceCell::::new() != OnceCell::from("value".to_owned())); } #[test] fn into_inner() { let cell: OnceCell = OnceCell::new(); assert_eq!(cell.into_inner(), None); let cell = OnceCell::new(); cell.set("hello".to_string()).unwrap(); assert_eq!(cell.into_inner(), Some("hello".to_string())); } #[test] fn debug_impl() { let cell = OnceCell::new(); assert_eq!(format!("{:#?}", cell), "OnceCell(Uninit)"); cell.set(vec!["hello", "world"]).unwrap(); assert_eq!( format!("{:#?}", cell), r#"OnceCell( [ "hello", "world", ], )"# ); } #[test] #[should_panic(expected = "reentrant init")] fn reentrant_init() { let x: OnceCell> = OnceCell::new(); let dangling_ref: Cell> = Cell::new(None); x.get_or_init(|| { let r = x.get_or_init(|| Box::new(92)); dangling_ref.set(Some(r)); Box::new(62) }); eprintln!("use after free: {:?}", dangling_ref.get().unwrap()); } #[test] fn aliasing_in_get() { let x = OnceCell::new(); x.set(42).unwrap(); let at_x = x.get().unwrap(); // --- (shared) borrow of inner `Option` --+ let _ = x.set(27); // <-- temporary (unique) borrow of inner `Option` | println!("{}", at_x); // <------- up until here ---------------------------+ } #[test] // https://github.com/rust-lang/rust/issues/34761#issuecomment-256320669 fn arrrrrrrrrrrrrrrrrrrrrr() { let cell = OnceCell::new(); { let s = String::new(); cell.set(&s).unwrap(); } }