Enum Flow 

#[non_exhaustive]
pub enum Flow {
    Tight,
    Relaxed,
}

The parts of a list row.

Four to begin with, taken from Balanced Breakfast, which was the only consumer that had all of them (row-primary, row-secondary, row-meta, row-actions). audiofiles has two and no slot structure at all, so it gains meta and actions as real work rather than a rename; goingson moves off task-row / task-cell.

Tokens joined at 0.9.0, and #[non_exhaustive] with it. See the crate header for why the two arrived together.

Meta against Tokens

The line is whether the thing has its own standing. Meta is one short trailing fact about the row, written as text: a count, a size, a date. Tokens is a set of small labelled things, each of which can be toned and can answer a click. “3 files” is meta. A status badge that is amber, and a tag you can click to filter by, are tokens.

Keeping them apart is what a single widened slot would have foreclosed. A renderer can right-align one string and cannot usefully do the same to a strip of chips, and a fact that is not clickable should not be drawn as though it were. How much vertical room a part’s text may take.

A row is an inline run and every part in it is a leaf, so a part’s text has always been drawn on one line and no description could say otherwise. Two apps say otherwise in their own stylesheets, both to the same number and both with a comment explaining it: Balanced Breakfast clamps a feed row’s title to two lines (.row--article .row-primary, whose comment reads “overrides .row-primary’s single flex line”), and goingson clamps a problem’s body to two (“two lines is enough to recognize one, and the full text is in the task once promoted”).

Two named tiers rather than a line count, and the count is what the measured demand argues against. Both sites want exactly one tier past the default, and a number invites a row whose primary is a paragraph, which is a block and has no business in a run. A third tier is a decision, made here, rather than something a call site can reach for.

What a renderer owes it: Tight is what a run already does and needs no answer. Relaxed is at most two lines and then truncation, however that renderer truncates – a webview clamps, a terminal wraps into two rows of cells, an immediate-mode renderer caps the galley. A renderer that cannot give two lines may draw one; what it may not do is grow without bound, because the run is a line and the row’s neighbours are relying on that.

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.

Tight

One line. What every part did before this type existed.

Relaxed

Up to two lines, then truncated.

Implementations

impl Flow

pub const fn lines(self) -> u8

How many lines the part may take.

A number here rather than in the enum, because a renderer needs one and a call site does not. That asymmetry is the whole argument for the tiers: the description says how much room the thing deserves and this says what that costs, so a third tier changes one line rather than every consumer’s arithmetic.

Trait Implementations

impl Clone for Flow

fn clone(&self) -> Flow

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Flow

impl Debug for Flow

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

Formats the value using the given formatter.

impl Default for Flow

fn default() -> Flow

Returns the “default value” for a type.

impl Eq for Flow

impl Hash for Flow

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 Flow

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for Flow