pub enum Reveal {
Expand description

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




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 x: <() as Assoc>::Output = true;

We also do not reveal the hidden type of opaque types during type-checking.



At codegen 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 auto traits and transmute-checking, which expose some details, but not the whole concrete type of the impl Trait.

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
Feeds this value into the given Hasher. Read more
Feeds a slice of this type into the given Hasher. Read more
This method tests for self and other values to be equal, and is used by ==. Read more
This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason. Read more
The entry point for folding. To fold a value t with a folder f call: t.try_fold_with(f). Read more
A convenient alternative to try_fold_with for use with infallible folders. Do not override this method, to ensure coherence with try_fold_with. Read more
The entry point for visiting. To visit a value t with a visitor v call: t.visit_with(v). Read more
Returns true if self has any late-bound regions that are either bound by binder or bound by some binder outside of binder. If binder is ty::INNERMOST, this indicates whether there are any late-bound regions that appear free. Read more
Returns true if this self has any regions that escape binder (and hence are not bound by it). Read more
“Free” regions in this context means that it has any region that is not (a) erased or (b) late-bound. Read more
True if there are any un-erased free regions.
Indicates whether this value references only ‘global’ generic parameters that are the same regardless of what fn we are in. This is used for caching. Read more
True if there are any late-bound regions
Indicates whether this value still has parameters/placeholders/inference variables which could be replaced later, in a way that would change the results of impl specialization. Read more

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

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The resulting type after obtaining ownership.
Creates owned data from borrowed data, usually by cloning. Read more
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.


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: 1 byte

Size for each variant:

  • UserFacing: 0 bytes
  • All: 0 bytes