Trait Constraint

Source

pub trait Constraint<Prim: PrimitiveType>:
    Display
    + Send
    + Sync
    + 'static {
    // Required methods
    fn visitor<'r>(
        &self,
        substitutions: &'r mut Substitutions<Prim>,
        errors: OpErrors<'r, Prim>,
    ) -> Box<dyn Visit<Prim> + 'r>;
    fn clone_boxed(&self) -> Box<dyn Constraint<Prim>>;
}

Expand description

Constraint that can be placed on Types.

Constraints can be placed on Function type variables, and can be applied to types in TypeArithmetic impls. For example, NumArithmetic places the Linearity constraint on types involved in arithmetic ops.

The constraint mechanism is similar to trait constraints in Rust, but is much more limited:

Constraints cannot be parametric (cf. parameters in traits, such AsRef<_> or Iterator<Item = _>).
Constraints are applied to types in separation; it is impossible to create a constraint involving several type variables.
Constraints cannot contradict each other.

§Implementation rules

Display must display constraint as an identifier (e.g., Lin). The string presentation of a constraint must be unique within a PrimitiveType; it is used to identify constraints in a ConstraintSet.

Required Methods§

Source

fn visitor<'r>( &self, substitutions: &'r mut Substitutions<Prim>, errors: OpErrors<'r, Prim>, ) -> Box<dyn Visit<Prim> + 'r>

Returns a Visitor that will be applied to constrained Types. The visitor may use substitutions to resolve types and errors to record constraint errors.