Enum AppearanceWrite 

#[non_exhaustive]
pub enum AppearanceWrite<T> {
    Refused,
    Accepted {
        was: Option<T>,
    },
}

What a SceneItem appearance setter did — and, when it did anything, the value it overwrote.

Why the old value comes out of the setter

ItemChange::AppearanceChanged carries an old, so a data layer can reverse a colour edit. That old has to come from somewhere, and the item is the only thing that has it: a fill lives inside the item, not on the scene entry.

The obvious shape — a fn fill(&self) -> Option<ColorProp> getter beside the setter — cannot be required, because most items have no fill slot at all, so it would have to be defaulted. A defaulted getter returning None would then report “there was no fill” for every third-party item that implements set_fill and forgets the getter, and an undone fill change would clear the fill instead of restoring it. Silent-wrong is the worst failure a journal can have.

Returning the old value from the setter has no default to get wrong: the code that overwrites the slot is the code that hands back what it overwrote, and the compiler will not let an implementor write one without the other. The default impl is Refused, which is exactly true of an item with no such slot and emits no change at all.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Refused

This item kind has no such slot, or rejected this particular value (TextItem always has a foreground colour, so it refuses a None fill). Nothing was written, and the scene emits no change.

Accepted

The slot took the value. was is what it held immediately before — None when the slot was empty.

Fields

was: Option<T>

The overwritten value, or None if the slot was empty.

Implementations

impl<T> AppearanceWrite<T>

pub fn replaced(previous: T) -> Self

Sugar for Accepted { was: Some(previous) }.

pub fn accepted(&self) -> bool

Whether the item took the write.

pub fn into_previous(self) -> Option<Option<T>>

The overwritten slot contents, or None when the write was refused.

The outer Option is “did anything happen”; the inner one is “was the slot occupied”.

Trait Implementations

impl<T: Clone> Clone for AppearanceWrite<T>

fn clone(&self) -> AppearanceWrite<T>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T: Debug> Debug for AppearanceWrite<T>

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

Formats the value using the given formatter.