Struct EqualityConstraint 

pub struct EqualityConstraint { /* private fields */ }

Constrains two variables to have the same value.

Used to express variable equality when two positions in a triple share the same logical variable but need distinct VariableIds for the TribleSetConstraint (which assumes its three positions have distinct ids).

The macro layer emits this automatically when a _?var appears in both the entity and value positions of the same triple.

Implementations

impl EqualityConstraint

pub fn new(a: VariableId, b: VariableId) -> Self

Creates a constraint requiring a and b to be bound to the same raw value.

Trait Implementations

impl<'c> Constraint<'c> for EqualityConstraint

fn estimate(&self, variable: VariableId, binding: &Binding) -> Option<usize>

Returns Some(1) when the peer variable is already bound (exactly one candidate). Returns None when the peer is unbound — the constraint has no independent opinion about the variable’s cardinality and defers to other constraints in the intersection. This is safe as long as each variable also appears in at least one other constraint (which the macro desugaring guarantees).

fn propose( &self, variable: VariableId, binding: &Binding, proposals: &mut Vec<RawValue>, )

When the peer variable is bound, proposes its value.

fn confirm( &self, variable: VariableId, binding: &Binding, proposals: &mut Vec<RawValue>, )

Retains only proposals that match the peer variable’s binding.

fn satisfied(&self, binding: &Binding) -> bool

Returns false when both variables are bound to different values.

fn variables(&self) -> VariableSet

Returns the set of variables this constraint touches.

fn influence(&self, variable: VariableId) -> VariableSet

Returns the set of variables whose estimates may change when variable is bound or unbound.