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

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Formats the value using the given formatter. Read more

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

This method tests for !=.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

This method turns the parameters of a DepNodeConstructor into an opaque Fingerprint to be used in DepNode. Not all DepNodeParams support being turned into a Fingerprint (they don’t need to if the corresponding DepNode is anonymous). Read more

This method tries to recover the query key from the given DepNode, something which is needed when forcing DepNodes during red-green evaluation. The query system will only call this method if fingerprint_style() is not FingerprintStyle::Opaque. It is always valid to return None here, in which case incremental compilation will treat the query as having changed instead of forcing it. Read more

Performs the conversion.

Performs the conversion.

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

🔬 This is a nightly-only experimental API. (toowned_clone_into)

Uses borrowed data to replace owned data, usually by cloning. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference’s “Type Layout” chapter for details on type layout guarantees.

Size: 72 bytes