Enum rustc_type_ir::Variance
source · pub enum Variance {
Covariant,
Invariant,
Contravariant,
Bivariant,
}
Variants§
Implementations§
source§impl Variance
impl Variance
sourcepub fn xform(self, v: Variance) -> Variance
pub fn xform(self, v: Variance) -> Variance
a.xform(b)
combines the variance of a context with the
variance of a type with the following meaning. If we are in a
context with variance a
, and we encounter a type argument in
a position with variance b
, then a.xform(b)
is the new
variance with which the argument appears.
Example 1:
*mut Vec<i32>
Here, the “ambient” variance starts as covariant. *mut T
is
invariant with respect to T
, so the variance in which the
Vec<i32>
appears is Covariant.xform(Invariant)
, which
yields Invariant
. Now, the type Vec<T>
is covariant with
respect to its type argument T
, and hence the variance of
the i32
here is Invariant.xform(Covariant)
, which results
(again) in Invariant
.
Example 2:
fn(*const Vec<i32>, *mut Vec<i32)
The ambient variance is covariant. A fn
type is
contravariant with respect to its parameters, so the variance
within which both pointer types appear is
Covariant.xform(Contravariant)
, or Contravariant
. *const T
is covariant with respect to T
, so the variance within
which the first Vec<i32>
appears is
Contravariant.xform(Covariant)
or Contravariant
. The same
is true for its i32
argument. In the *mut T
case, the
variance of Vec<i32>
is Contravariant.xform(Invariant)
,
and hence the outermost type is Invariant
with respect to
Vec<i32>
(and its i32
argument).
Source: Figure 1 of “Taming the Wildcards: Combining Definition- and Use-Site Variance” published in PLDI’11.
Trait Implementations§
source§impl<__D: SpanDecoder> Decodable<__D> for Variance
impl<__D: SpanDecoder> Decodable<__D> for Variance
source§impl<__E: SpanEncoder> Encodable<__E> for Variance
impl<__E: SpanEncoder> Encodable<__E> for Variance
source§impl<__CTX> HashStable<__CTX> for Variance
impl<__CTX> HashStable<__CTX> for Variance
fn hash_stable(&self, __hcx: &mut __CTX, __hasher: &mut StableHasher)
source§impl PartialEq for Variance
impl PartialEq for Variance
source§impl<I: Interner> TypeFoldable<I> for Variance
impl<I: Interner> TypeFoldable<I> for Variance
source§fn try_fold_with<F: FallibleTypeFolder<I>>(
self,
_: &mut F,
) -> Result<Self, F::Error>
fn try_fold_with<F: FallibleTypeFolder<I>>( self, _: &mut F, ) -> Result<Self, F::Error>
source§fn fold_with<F: TypeFolder<I>>(self, _: &mut F) -> Self
fn fold_with<F: TypeFolder<I>>(self, _: &mut F) -> Self
try_fold_with
for use with infallible
folders. Do not override this method, to ensure coherence with
try_fold_with
.source§impl<I: Interner> TypeVisitable<I> for Variance
impl<I: Interner> TypeVisitable<I> for Variance
source§fn visit_with<F: TypeVisitor<I>>(&self, _: &mut F) -> F::Result
fn visit_with<F: TypeVisitor<I>>(&self, _: &mut F) -> F::Result
impl Copy for Variance
impl Eq for Variance
impl StructuralPartialEq for Variance
Auto Trait Implementations§
impl Freeze for Variance
impl RefUnwindSafe for Variance
impl Send for Variance
impl Sync for Variance
impl Unpin for Variance
impl UnwindSafe for Variance
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
source§impl<T> CloneToUninit for Twhere
T: Copy,
impl<T> CloneToUninit for Twhere
T: Copy,
source§unsafe fn clone_to_uninit(&self, dst: *mut T)
unsafe fn clone_to_uninit(&self, dst: *mut T)
clone_to_uninit
)source§impl<T> CloneToUninit for Twhere
T: Clone,
impl<T> CloneToUninit for Twhere
T: Clone,
source§default unsafe fn clone_to_uninit(&self, dst: *mut T)
default unsafe fn clone_to_uninit(&self, dst: *mut T)
clone_to_uninit
)source§impl<T, R> CollectAndApply<T, R> for T
impl<T, R> CollectAndApply<T, R> for T
source§impl<Q, K> Equivalent<K> for Q
impl<Q, K> Equivalent<K> for Q
source§impl<Q, K> Equivalent<K> for Q
impl<Q, K> Equivalent<K> for Q
source§impl<Q, K> Equivalent<K> for Q
impl<Q, K> Equivalent<K> for Q
source§fn equivalent(&self, key: &K) -> bool
fn equivalent(&self, key: &K) -> bool
key
and return true
if they are equal.source§impl<T> Instrument for T
impl<T> Instrument for T
source§fn instrument(self, span: Span) -> Instrumented<Self>
fn instrument(self, span: Span) -> Instrumented<Self>
source§fn in_current_span(self) -> Instrumented<Self>
fn in_current_span(self) -> Instrumented<Self>
source§impl<T> IntoEither for T
impl<T> IntoEither for T
source§fn into_either(self, into_left: bool) -> Either<Self, Self>
fn into_either(self, into_left: bool) -> Either<Self, Self>
self
into a Left
variant of Either<Self, Self>
if into_left
is true
.
Converts self
into a Right
variant of Either<Self, Self>
otherwise. Read moresource§fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
self
into a Left
variant of Either<Self, Self>
if into_left(&self)
returns true
.
Converts self
into a Right
variant of Either<Self, Self>
otherwise. Read moresource§impl<I, T> TypeVisitableExt<I> for Twhere
I: Interner,
T: TypeVisitable<I>,
impl<I, T> TypeVisitableExt<I> for Twhere
I: Interner,
T: TypeVisitable<I>,
fn has_type_flags(&self, flags: TypeFlags) -> bool
source§fn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool
fn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool
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.fn error_reported(&self) -> Result<(), <I as Interner>::ErrorGuaranteed>
source§fn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool
fn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool
true
if this type has any regions that escape binder
(and
hence are not bound by it).source§fn has_escaping_bound_vars(&self) -> bool
fn has_escaping_bound_vars(&self) -> bool
true
if this type has regions that are not a part of the type.
For example, for<'a> fn(&'a i32)
return false
, while fn(&'a i32)
would return true
. The latter can occur when traversing through the
former. Read morefn has_aliases(&self) -> bool
fn has_inherent_projections(&self) -> bool
fn has_opaque_types(&self) -> bool
fn has_coroutines(&self) -> bool
fn references_error(&self) -> bool
fn has_non_region_param(&self) -> bool
fn has_infer_regions(&self) -> bool
fn has_infer_types(&self) -> bool
fn has_non_region_infer(&self) -> bool
fn has_infer(&self) -> bool
fn has_placeholders(&self) -> bool
fn has_non_region_placeholders(&self) -> bool
fn has_param(&self) -> bool
source§fn has_free_regions(&self) -> bool
fn has_free_regions(&self) -> bool
fn has_erased_regions(&self) -> bool
source§fn has_erasable_regions(&self) -> bool
fn has_erasable_regions(&self) -> bool
source§fn is_global(&self) -> bool
fn is_global(&self) -> bool
source§fn has_bound_regions(&self) -> bool
fn has_bound_regions(&self) -> bool
source§fn has_non_region_bound_vars(&self) -> bool
fn has_non_region_bound_vars(&self) -> bool
source§fn has_bound_vars(&self) -> bool
fn has_bound_vars(&self) -> bool
source§fn still_further_specializable(&self) -> bool
fn still_further_specializable(&self) -> bool
impl
specialization.source§impl<I, T, U> Upcast<I, U> for Twhere
U: UpcastFrom<I, T>,
impl<I, T, U> Upcast<I, U> for Twhere
U: UpcastFrom<I, T>,
source§impl<I, T> UpcastFrom<I, T> for T
impl<I, T> UpcastFrom<I, T> for T
fn upcast_from(from: T, _tcx: I) -> T
source§impl<T> WithSubscriber for T
impl<T> WithSubscriber for T
source§fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
source§fn with_current_subscriber(self) -> WithDispatch<Self>
fn with_current_subscriber(self) -> WithDispatch<Self>
impl<'a, T> Captures<'a> for Twhere
T: ?Sized,
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:
Covariant
: 0 bytesInvariant
: 0 bytesContravariant
: 0 bytesBivariant
: 0 bytes