Add a public constructor for Mut<T>

crates/bevy_ecs/src/change_detection.rs

@@ -537,6 +537,41 @@ pub struct Mut<'a, T: ?Sized> {
  pub(crate) ticks: TicksMut<'a>,
 }
 
+impl<'a, T: ?Sized> Mut<'a, T> {
+ /// Creates a new change-detection enabled smart pointer.
+ /// In almost all cases you do not need to call this method manually,
+ /// as instances of `Mut` will be created by engine-internal code.
+ ///
+ /// Many use-cases of this method would be better served by [`Mut::map_unchanged`]
+ /// or [`Mut::reborrow`].
+ ///
+ /// - `value` - The value wrapped by this smart pointer.
+ /// - `added` - A [`Tick`] that stores the tick when the wrapped value was created.
+ /// - `last_changed` - A [`Tick`] that stores the last time the wrapped value was changed.
+ /// This will be updated to the value of `change_tick` if the returned smart pointer
+ /// is modified.
+ /// - `last_change_tick` - A [`Tick`], occurring before `change_tick`, which is used
+ /// as a reference to determine whether the wrapped value is newly added or changed.
+ /// - `change_tick` - A [`Tick`] corresponding to the current point in time -- "now".
+ pub fn new(
+ value: &'a mut T,
+ added: &'a mut Tick,
+ last_changed: &'a mut Tick,
+ last_change_tick: u32,
+ change_tick: u32,
+ ) -> Self {
+ Self {
+ value,
+ ticks: TicksMut {
+ added,
+ changed: last_changed,
+ last_change_tick,
+ change_tick,
+ },
+ }
+ }
+}
+
 impl<'a, T: ?Sized> From<Mut<'a, T>> for Ref<'a, T> {
  fn from(mut_ref: Mut<'a, T>) -> Self {
  Self {
@@ -827,6 +862,26 @@ mod tests {
  assert_eq!(4, into_mut.ticks.change_tick);
  }
 
+ #[test]
+ fn mut_new() {
+ let mut component_ticks = ComponentTicks {
+ added: Tick::new(1),
+ changed: Tick::new(3),
+ };
+ let mut res = R {};
+
+ let val = Mut::new(
+ &mut res,
+ &mut component_ticks.added,
+ &mut component_ticks.changed,
+ 2, // last_change_tick
+ 4, // current change_tick
+ );
+
+ assert!(!val.is_added());
+ assert!(val.is_changed());
+ }
+
  #[test]
  fn mut_from_non_send_mut() {
  let mut component_ticks = ComponentTicks {