Struct rustc_mir_build::thir::pattern::Ascription

pub struct Ascription<'tcx> {
    pub user_ty: PatTyProj<'tcx>,
    pub variance: Variance,
    pub user_ty_span: Span,
}

Fields

user_ty: PatTyProj<'tcx>

variance: Variance

Variance to use when relating the type user_ty to the type of the value being matched. Typically, this is Variance::Covariant, since the value being matched must have a type that is some subtype of the ascribed type.

Note that this variance does not apply for any bindings within subpatterns. The type assigned to those bindings must be exactly equal to the user_ty given here.

The only place where this field is not Covariant is when matching constants, where we currently use Contravariant – this is because the constant type just needs to be “comparable” to the type of the input value. So, for example:

match x { "foo" => .. }

requires that &'static str <: T_x, where T_x is the type of x. Really, we should probably be checking for a PartialEq impl instead, but this preserves the behavior of the old type-check for now. See #57280 for details.

user_ty_span: Span

Trait Implementations

impl<'tcx> Clone for Ascription<'tcx>

fn clone(&self) -> Ascription<'tcx>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<'tcx> Debug for Ascription<'tcx>

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

Formats the value using the given formatter.

impl<'tcx> PartialEq<Ascription<'tcx>> for Ascription<'tcx>

fn eq(&self, other: &Ascription<'tcx>) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Ascription<'tcx>) -> bool

This method tests for !=.

impl<'tcx> Copy for Ascription<'tcx>

impl<'tcx> StructuralPartialEq for Ascription<'tcx>