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 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83
use std::marker::PhantomData;
use crate::{
cell::{AtomicRefCell, AtomicRefMut},
world::{FetchMut, Resource, ResourceId},
};
type StdEntry<'a, K, V> = std::collections::hash_map::Entry<'a, K, V>;
/// An entry to a resource of the `World` struct.
/// This is similar to the Entry API found in the standard library.
///
/// ## Examples
///
/// ```
/// use shred::World;
///
/// #[derive(Debug)]
/// struct Res(i32);
///
/// let mut world = World::empty();
///
/// let value = world.entry().or_insert(Res(4));
/// println!("{:?}", value.0 * 2);
/// ```
pub struct Entry<'a, T: 'a> {
inner: StdEntry<'a, ResourceId, AtomicRefCell<Box<dyn Resource>>>,
marker: PhantomData<T>,
}
impl<'a, T> Entry<'a, T>
where
T: Resource + 'a,
{
/// Returns this entry's value, inserts and returns `v` otherwise.
///
/// Please note that you should use `or_insert_with` in case the creation of
/// the value is expensive.
pub fn or_insert(self, v: T) -> FetchMut<'a, T> {
self.or_insert_with(move || v)
}
/// Returns this entry's value, inserts and returns the return value of `f`
/// otherwise.
pub fn or_insert_with<F>(self, f: F) -> FetchMut<'a, T>
where
F: FnOnce() -> T,
{
let value = self
.inner
.or_insert_with(move || AtomicRefCell::new(Box::new(f())));
let inner = AtomicRefMut::map(value.borrow_mut(), Box::as_mut);
FetchMut {
inner,
phantom: PhantomData,
}
}
}
pub(super) fn create_entry<T>(
e: StdEntry<ResourceId, AtomicRefCell<Box<dyn Resource>>>,
) -> Entry<T> {
Entry {
inner: e,
marker: PhantomData,
}
}
#[cfg(test)]
mod tests {
use crate::world::World;
#[test]
fn test_entry() {
struct Res;
let mut world = World::empty();
world.entry().or_insert(Res);
assert!(world.has_value::<Res>());
}
}