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§

Blanket Implementations§

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impl<T> Any for Twhere 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 Twhere 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 Twhere 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 Twhere 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 Twhere 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 Twhere 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 Twhere 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