Enum rustc_typeck::check::Expectation

pub enum Expectation<'tcx> {
    NoExpectation,
    ExpectIfCondition,
    ExpectHasType(Ty<'tcx>),
    ExpectCastableToType(Ty<'tcx>),
    ExpectRvalueLikeUnsized(Ty<'tcx>),
}

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

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When type-checking an expression, we propagate downward whatever type hint we are able in the form of an Expectation.

Variants

NoExpectation

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

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We know nothing about what type this expression should have.

ExpectIfCondition

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

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This expression is an if condition, it must resolve to bool.

ExpectHasType(Ty<'tcx>)

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

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This expression should have the type given (or some subtype)

ExpectCastableToType(Ty<'tcx>)

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

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This expression will be cast to the Ty

ExpectRvalueLikeUnsized(Ty<'tcx>)

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

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

This rvalue expression will be wrapped in & or Box and coerced to &Ty or Box<Ty>, respectively. Ty is [A] or Trait.

Methods

impl<'a, 'gcx, 'tcx> Expectation<'tcx>

fn adjust_for_branches(&self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) -> Expectation<'tcx>

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fn rvalue_hint(fcx: &FnCtxt<'a, 'gcx, 'tcx>, ty: Ty<'tcx>) -> Expectation<'tcx>

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

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Provide an expectation for an rvalue expression given an optional hint, which is not required for type safety (the resulting type might be checked higher up, as is the case with &expr and box expr), but is useful in determining the concrete type.

The primary use case is where the expected type is a fat pointer, like &[isize]. For example, consider the following statement:

let x: &[isize] = &[1, 2, 3];

In this case, the expected type for the &[1, 2, 3] expression is &[isize]. If however we were to say that [1, 2, 3] has the expectation ExpectHasType([isize]), that would be too strong -- [1, 2, 3] does not have the type [isize] but rather [isize; 3]. It is only the &[1, 2, 3] expression as a whole that can be coerced to the type &[isize]. Therefore, we propagate this more limited hint, which still is useful, because it informs integer literals and the like. See the test case test/run-pass/coerce-expect-unsized.rs and #20169 for examples of where this comes up,.

fn resolve(self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) -> Expectation<'tcx>

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fn to_option(self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) -> Option<Ty<'tcx>>

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

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fn only_has_type(self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) -> Option<Ty<'tcx>>

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

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It sometimes happens that we want to turn an expectation into a hard constraint (i.e., something that must be satisfied for the program to type-check). only_has_type will return such a constraint, if it exists.

fn coercion_target_type(     self,     fcx: &FnCtxt<'a, 'gcx, 'tcx>,     span: Span ) -> Ty<'tcx>

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

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Like only_has_type, but instead of returning None if no hard constraint exists, creates a fresh type variable.

Trait Implementations

impl<'tcx> Copy for Expectation<'tcx>

impl<'tcx> Clone for Expectation<'tcx>

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

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<'tcx> Debug for Expectation<'tcx>

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

Formats the value using the given formatter.