bevy_utils/lib.rs
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#![cfg_attr(docsrs, feature(doc_auto_cfg))]
#![doc(
html_logo_url = "https://bevyengine.org/assets/icon.png",
html_favicon_url = "https://bevyengine.org/assets/icon.png"
)]
#![no_std]
//! General utilities for first-party [Bevy] engine crates.
//!
//! [Bevy]: https://bevyengine.org/
#[cfg(feature = "std")]
extern crate std;
#[cfg(feature = "alloc")]
extern crate alloc;
/// The utilities prelude.
///
/// This includes the most common types in this crate, re-exported for your convenience.
pub mod prelude {
pub use crate::default;
}
pub mod synccell;
pub mod syncunsafecell;
mod default;
mod once;
#[cfg(feature = "std")]
mod parallel_queue;
#[doc(hidden)]
pub use once::OnceFlag;
pub use default::default;
#[cfg(feature = "std")]
pub use parallel_queue::*;
use core::mem::ManuallyDrop;
#[cfg(feature = "alloc")]
use {
bevy_platform::{
collections::HashMap,
hash::{Hashed, NoOpHash, PassHash},
},
core::{any::TypeId, hash::Hash},
};
/// A [`HashMap`] pre-configured to use [`Hashed`] keys and [`PassHash`] passthrough hashing.
/// Iteration order only depends on the order of insertions and deletions.
#[cfg(feature = "alloc")]
pub type PreHashMap<K, V> = HashMap<Hashed<K>, V, PassHash>;
/// Extension methods intended to add functionality to [`PreHashMap`].
#[cfg(feature = "alloc")]
pub trait PreHashMapExt<K, V> {
/// Tries to get or insert the value for the given `key` using the pre-computed hash first.
/// If the [`PreHashMap`] does not already contain the `key`, it will clone it and insert
/// the value returned by `func`.
fn get_or_insert_with<F: FnOnce() -> V>(&mut self, key: &Hashed<K>, func: F) -> &mut V;
}
#[cfg(feature = "alloc")]
impl<K: Hash + Eq + PartialEq + Clone, V> PreHashMapExt<K, V> for PreHashMap<K, V> {
#[inline]
fn get_or_insert_with<F: FnOnce() -> V>(&mut self, key: &Hashed<K>, func: F) -> &mut V {
use bevy_platform::collections::hash_map::RawEntryMut;
let entry = self
.raw_entry_mut()
.from_key_hashed_nocheck(key.hash(), key);
match entry {
RawEntryMut::Occupied(entry) => entry.into_mut(),
RawEntryMut::Vacant(entry) => {
let (_, value) = entry.insert_hashed_nocheck(key.hash(), key.clone(), func());
value
}
}
}
}
/// A specialized hashmap type with Key of [`TypeId`]
/// Iteration order only depends on the order of insertions and deletions.
#[cfg(feature = "alloc")]
pub type TypeIdMap<V> = HashMap<TypeId, V, NoOpHash>;
/// A type which calls a function when dropped.
/// This can be used to ensure that cleanup code is run even in case of a panic.
///
/// Note that this only works for panics that [unwind](https://doc.rust-lang.org/nomicon/unwinding.html)
/// -- any code within `OnDrop` will be skipped if a panic does not unwind.
/// In most cases, this will just work.
///
/// # Examples
///
/// ```
/// # use bevy_utils::OnDrop;
/// # fn test_panic(do_panic: bool, log: impl FnOnce(&str)) {
/// // This will print a message when the variable `_catch` gets dropped,
/// // even if a panic occurs before we reach the end of this scope.
/// // This is similar to a `try ... catch` block in languages such as C++.
/// let _catch = OnDrop::new(|| log("Oops, a panic occurred and this function didn't complete!"));
///
/// // Some code that may panic...
/// // ...
/// # if do_panic { panic!() }
///
/// // Make sure the message only gets printed if a panic occurs.
/// // If we remove this line, then the message will be printed regardless of whether a panic occurs
/// // -- similar to a `try ... finally` block.
/// core::mem::forget(_catch);
/// # }
/// #
/// # test_panic(false, |_| unreachable!());
/// # let mut did_log = false;
/// # std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| {
/// # test_panic(true, |_| did_log = true);
/// # }));
/// # assert!(did_log);
/// ```
pub struct OnDrop<F: FnOnce()> {
callback: ManuallyDrop<F>,
}
impl<F: FnOnce()> OnDrop<F> {
/// Returns an object that will invoke the specified callback when dropped.
pub fn new(callback: F) -> Self {
Self {
callback: ManuallyDrop::new(callback),
}
}
}
impl<F: FnOnce()> Drop for OnDrop<F> {
fn drop(&mut self) {
#![expect(
unsafe_code,
reason = "Taking from a ManuallyDrop requires unsafe code."
)]
// SAFETY: We may move out of `self`, since this instance can never be observed after it's dropped.
let callback = unsafe { ManuallyDrop::take(&mut self.callback) };
callback();
}
}
#[cfg(test)]
mod tests {
use super::*;
use static_assertions::assert_impl_all;
// Check that the HashMaps are Clone if the key/values are Clone
assert_impl_all!(PreHashMap::<u64, usize>: Clone);
#[test]
fn fast_typeid_hash() {
struct Hasher;
impl core::hash::Hasher for Hasher {
fn finish(&self) -> u64 {
0
}
fn write(&mut self, _: &[u8]) {
panic!("Hashing of core::any::TypeId changed");
}
fn write_u64(&mut self, _: u64) {}
}
Hash::hash(&TypeId::of::<()>(), &mut Hasher);
}
#[cfg(feature = "alloc")]
#[test]
fn stable_hash_within_same_program_execution() {
use alloc::vec::Vec;
let mut map_1 = <HashMap<_, _>>::default();
let mut map_2 = <HashMap<_, _>>::default();
for i in 1..10 {
map_1.insert(i, i);
map_2.insert(i, i);
}
assert_eq!(
map_1.iter().collect::<Vec<_>>(),
map_2.iter().collect::<Vec<_>>()
);
}
}