Enum Showing 

#[non_exhaustive]
pub enum Showing {
    All,
    One,
    AtMostOne,
}

How many of a region’s children are visible at once.

One sentence covering three shapes: this region holds several children and shows some of them, and the reader can change which. A tab group, a carousel and a disclosure all need it, and without it a renderer has two moves: hardcode a widget name, or draw every child. That is what puts per-widget code in renderers.

What is here and what is not

The kind, and only the kind. Which child is currently up is the current answer, and a layer that defers every address does not hold the current answer either — the split Selector already makes, where this crate says what kind of chooser a thing is and the router says which option is picked. So a holder of regions carries the index and the per-child label beside this.

What a renderer does with it

Derives its chrome, once, for every widget rather than per name:

• Children carrying labels get a strip of the labels, the current one marked.
• Children carrying none get previous, position, next.
• AtMostOne over one child gets a summary line that opens.

The name on Region::Widget survives as app vocabulary, for a renderer that wants to do something special with one, which is what it should have been from the start.

Degradation runs the way it already did: a renderer ignoring this draws every child, which is more content rather than less.

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.

All

Every child, in order. What every region did before this existed.

One

Exactly one. A carousel, a tab group.

AtMostOne

One, or none. A disclosure, which is closed until it is opened.

Implementations

impl Showing

pub const fn selective(self) -> bool

Whether the reader can change which child is up.

The question every renderer’s region arm asks before deriving any chrome, and a method rather than a matches! at each renderer for Region::name’s reason: three renderers writing the same comparison is how they come to disagree about a member added later.

pub const fn dismissible(self) -> bool

Whether showing nothing is a legal state.

True only for AtMostOne. A renderer needs this to know whether its control closes as well as moves: a carousel’s row moves between frames and never reaches empty, and a disclosure’s summary line is the same control wearing its closed state.

Trait Implementations

impl Clone for Showing

fn clone(&self) -> Showing

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Showing

impl Debug for Showing

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

Formats the value using the given formatter.

impl Default for Showing

fn default() -> Showing

Returns the “default value” for a type.

impl Eq for Showing

impl Hash for Showing

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for Showing

fn eq(&self, other: &Showing) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Showing