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3cddc8bff6
The signature for new was ``` fn new<F>(f: F) -> Lazy<T, F> ``` Notably, with `F` unconstrained, `T` can be literally anything, and just `let _ = Lazy::new(|| 92)` would not typecheck. This historiacally was a necessity -- `new` is a `const` function, it couldn't have any bounds. Today though, we can move `new` under the `F: FnOnce() -> T` bound, which gives the compiler enough data to infer the type of T from closure.
145 lines
3.3 KiB
Rust
145 lines
3.3 KiB
Rust
use core::{
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cell::{Cell, LazyCell, OnceCell},
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sync::atomic::{AtomicUsize, Ordering::SeqCst},
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};
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#[test]
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fn once_cell() {
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let c = OnceCell::new();
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assert!(c.get().is_none());
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c.get_or_init(|| 92);
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assert_eq!(c.get(), Some(&92));
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c.get_or_init(|| panic!("Kabom!"));
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assert_eq!(c.get(), Some(&92));
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}
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#[test]
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fn once_cell_get_mut() {
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let mut c = OnceCell::new();
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assert!(c.get_mut().is_none());
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c.set(90).unwrap();
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*c.get_mut().unwrap() += 2;
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assert_eq!(c.get_mut(), Some(&mut 92));
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}
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#[test]
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fn once_cell_drop() {
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static DROP_CNT: AtomicUsize = AtomicUsize::new(0);
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struct Dropper;
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impl Drop for Dropper {
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fn drop(&mut self) {
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DROP_CNT.fetch_add(1, SeqCst);
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}
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}
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let x = OnceCell::new();
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x.get_or_init(|| Dropper);
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assert_eq!(DROP_CNT.load(SeqCst), 0);
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drop(x);
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assert_eq!(DROP_CNT.load(SeqCst), 1);
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}
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#[test]
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fn unsync_once_cell_drop_empty() {
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let x = OnceCell::<&'static str>::new();
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drop(x);
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}
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#[test]
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const fn once_cell_const() {
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let _once_cell: OnceCell<u32> = OnceCell::new();
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let _once_cell: OnceCell<u32> = OnceCell::from(32);
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}
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#[test]
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fn clone() {
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let s = OnceCell::new();
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let c = s.clone();
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assert!(c.get().is_none());
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s.set("hello").unwrap();
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let c = s.clone();
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assert_eq!(c.get().map(|c| *c), Some("hello"));
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}
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#[test]
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fn from_impl() {
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assert_eq!(OnceCell::from("value").get(), Some(&"value"));
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assert_ne!(OnceCell::from("foo").get(), Some(&"bar"));
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}
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#[test]
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fn partialeq_impl() {
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assert!(OnceCell::from("value") == OnceCell::from("value"));
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assert!(OnceCell::from("foo") != OnceCell::from("bar"));
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assert!(OnceCell::<&'static str>::new() == OnceCell::new());
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assert!(OnceCell::<&'static str>::new() != OnceCell::from("value"));
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}
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#[test]
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fn into_inner() {
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let cell: OnceCell<&'static str> = OnceCell::new();
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assert_eq!(cell.into_inner(), None);
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let cell = OnceCell::new();
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cell.set("hello").unwrap();
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assert_eq!(cell.into_inner(), Some("hello"));
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}
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#[test]
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fn lazy_new() {
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let called = Cell::new(0);
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let x = LazyCell::new(|| {
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called.set(called.get() + 1);
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92
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});
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assert_eq!(called.get(), 0);
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let y = *x - 30;
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assert_eq!(y, 62);
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assert_eq!(called.get(), 1);
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let y = *x - 30;
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assert_eq!(y, 62);
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assert_eq!(called.get(), 1);
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}
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// Check that we can infer `T` from closure's type.
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#[test]
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fn lazy_type_inference() {
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let _ = LazyCell::new(|| ());
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}
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#[test]
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fn aliasing_in_get() {
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let x = OnceCell::new();
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x.set(42).unwrap();
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let at_x = x.get().unwrap(); // --- (shared) borrow of inner `Option<T>` --+
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let _ = x.set(27); // <-- temporary (unique) borrow of inner `Option<T>` |
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println!("{at_x}"); // <------- up until here ---------------------------+
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}
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#[test]
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#[should_panic(expected = "reentrant init")]
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fn reentrant_init() {
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let x: OnceCell<Box<i32>> = OnceCell::new();
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let dangling_ref: Cell<Option<&i32>> = Cell::new(None);
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x.get_or_init(|| {
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let r = x.get_or_init(|| Box::new(92));
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dangling_ref.set(Some(r));
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Box::new(62)
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});
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eprintln!("use after free: {:?}", dangling_ref.get().unwrap());
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}
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#[test]
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fn dropck() {
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let cell = OnceCell::new();
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{
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let s = String::new();
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cell.set(&s).unwrap();
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}
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}
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