Enum rustc_trait_selection::traits::Reveal
source · pub enum Reveal {
UserFacing,
All,
}
Expand description
Depending on the stage of compilation, we want projection to be more or less conservative.
Variants§
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.
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§
impl RefUnwindSafe for Reveal
impl Send for Reveal
impl Sync for Reveal
impl Unpin for Reveal
impl UnwindSafe for Reveal
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
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 bytesAll
: 0 bytes