Struct HandlerReplacement 

#[non_exhaustive]
pub struct HandlerReplacement {
    pub old: Option<SceneItemHandlerSet>,
    pub new: Option<SceneItemHandlerSet>,
}

The two sides of a Scene::set_item_handlers, as they ride an ItemChange::HandlersChanged.

None on either side means “no handler set at all”, which is a state an item can be in and is distinct from an empty one.

SceneItemHandlerSet stores its closures as Rc<dyn Fn>, so carrying both sides is a handful of refcount bumps rather than a deep copy — which is why this could be carried and, until it was, simply was not.

#[non_exhaustive]: this crate has out-of-tree consumers.

Fields (Non-exhaustive)

Non-exhaustive structs could have additional fields added in future. Therefore, non-exhaustive structs cannot be constructed in external crates using the traditional Struct { .. } syntax; cannot be matched against without a wildcard ..; and struct update syntax will not work.

old: Option<SceneItemHandlerSet>

What the item had before. None when it had none.

new: Option<SceneItemHandlerSet>

What it has now. None when the call cleared them.

Trait Implementations

impl Clone for HandlerReplacement

fn clone(&self) -> HandlerReplacement

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for HandlerReplacement

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Hand-written: SceneItemHandlerSet holds Rc<dyn Fn> closures and is not Debug, and ItemChange is. Reports which side was present, which is the part of a handler swap that reads usefully in a log — the same call the hand-written Debug for RemovedItem makes about its magnets.