Enum rustc::traits::Reveal

pub enum Reveal {
    UserFacing,
    All,
}

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Depending on the stage of compilation, we want projection to be more or less conservative.

Variants

UserFacing

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At type-checking time, we refuse to project any associated type that is marked default. Non-default ("final") types are always projected. This is necessary in general for soundness of specialization. However, we could allow projections in fully-monomorphic cases. We choose not to, because we prefer for default type to force the type definition to be treated abstractly by any consumers of the impl. Concretely, that means that the following example will fail to compile:

trait Assoc {
    type Output;
}

impl<T> Assoc for T {
    default type Output = bool;
}

fn main() {
    let <() as Assoc>::Output = true;
}

All

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At trans time, all monomorphic projections will succeed. Also, impl Trait is normalized to the concrete type, which has to be already collected by type-checking.

NOTE: As impl Trait's concrete type should never be observable directly by the user, Reveal::All should not be used by checks which may expose type equality or type contents to the user. There are some exceptions, e.g. around OIBITS and transmute-checking, which expose some details, but not the whole concrete type of the impl Trait.

Trait Implementations

impl<'tcx> HashStable<StableHashingContext<'tcx>> for Reveal

fn hash_stable<W: StableHasherResult>(
    &self,
    __ctx: &mut StableHashingContext<'tcx>,
    __hasher: &mut StableHasher<W>
)

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impl Debug for Reveal

fn fmt(&self, __arg_0: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Copy for Reveal

impl Clone for Reveal

fn clone(&self) -> Reveal

Returns a copy of the value.

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

Performs copy-assignment from source.

impl PartialEq for Reveal

fn eq(&self, __arg_0: &Reveal) -> bool

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

fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl Eq for Reveal

impl Hash for Reveal

fn hash<__H: Hasher>(&self, __arg_0: &mut __H)

Feeds this value into the given [Hasher].

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given [Hasher].

impl<'tcx> Lift<'tcx> for Reveal

type Lifted = Self

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fn lift_to_tcx<'a, 'gcx>(&self, _: TyCtxt<'a, 'gcx, 'tcx>) -> Option<Self>

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impl<'tcx> TypeFoldable<'tcx> for Reveal

fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(
    &self,
    _: &mut F
) -> Reveal

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fn super_visit_with<F: TypeVisitor<'tcx>>(&self, _: &mut F) -> bool

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fn fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(
    &self,
    folder: &mut F
) -> Self

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fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool

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fn has_regions_escaping_depth(&self, depth: u32) -> bool

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fn has_escaping_regions(&self) -> bool

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fn has_type_flags(&self, flags: TypeFlags) -> bool

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fn has_projections(&self) -> bool

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fn references_error(&self) -> bool

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fn has_param_types(&self) -> bool

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fn has_self_ty(&self) -> bool

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fn has_infer_types(&self) -> bool

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fn needs_infer(&self) -> bool

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fn needs_subst(&self) -> bool

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fn has_re_skol(&self) -> bool

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fn has_closure_types(&self) -> bool

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fn has_erasable_regions(&self) -> bool

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fn is_normalized_for_trans(&self) -> bool

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fn is_global(&self) -> bool

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Indicates whether this value references only 'global' types/lifetimes that are the same regardless of what fn we are in. This is used for caching. Errs on the side of returning false.