# Enum rustc_infer::traits::project::Reveal

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    pub enum Reveal {
        UserFacing,
        All,
    }

Expand description

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

## Variants§

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### UserFacing

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:

ⓘ

    #![feature(specialization)]
    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.

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### All

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`.

## Auto Trait Implementations§

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### impl RefUnwindSafe for Reveal

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### impl Send for Reveal

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### impl Sync for Reveal

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### impl Unpin for Reveal

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### impl UnwindSafe for Reveal

## Blanket Implementations§

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### impl<T> Any for T
where T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T
where U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

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

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### impl<T> ToOwned for T
where T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::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: 1 byte

Size for each variant:

- `UserFacing`: 0 bytes
- `All`: 0 bytes