Enum Absent 

pub enum Absent {
    Resolves(Resolution, Produced, Taken),
    Silent(Silence, Substitute),
}

What the engine does when the label is missing.

The engine’s finding and this crate’s substitute are facts about different actors, and one slot cannot hold both without one standing in for the other. Splitting them is also what makes a substitute unrepresentable where the engine already has a value: Absent::Resolves has no room for one.

Variants

Resolves(Resolution, Produced, Taken)

The engine resolves the missing label to a value.

Taken says whether this crate’s reader takes it. There is no slot for a value of its own: a reader either takes the engine’s or keeps the absence, so a third answer stays unrepresentable.

Silent(Silence, Substitute)

The engine’s answer names no value, so the reader decides for itself.

Trait Implementations

impl Clone for Absent

fn clone(&self) -> Absent

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Absent

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

Formats the value using the given formatter.

impl PartialEq for Absent

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for Absent

impl StructuralPartialEq for Absent