Enum chalk_ir::Variance [−][src]
pub enum Variance { Covariant, Invariant, Contravariant, }
Expand description
Variance
Variants
a <: b
a == b
b <: a
Implementations
impl Variance
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impl Variance
[src]pub fn xform(self, other: Variance) -> Variance
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pub fn xform(self, other: Variance) -> Variance
[src]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. (Doc from rustc)
Trait Implementations
impl Copy for Variance
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impl Eq for Variance
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impl StructuralEq for Variance
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impl StructuralPartialEq for Variance
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Auto Trait Implementations
impl RefUnwindSafe for Variance
impl Send for Variance
impl Sync for Variance
impl Unpin for Variance
impl UnwindSafe for Variance
Blanket Implementations
impl<T> BorrowMut<T> for T where
T: ?Sized,
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impl<T> BorrowMut<T> for T where
T: ?Sized,
[src]pub fn borrow_mut(&mut self) -> &mut T
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pub fn borrow_mut(&mut self) -> &mut T
[src]Mutably borrows from an owned value. Read more
impl<T> Cast for T
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impl<T> Cast for T
[src]fn cast<U>(self, interner: &U::Interner) -> U where
Self: CastTo<U>,
U: HasInterner,
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fn cast<U>(self, interner: &U::Interner) -> U where
Self: CastTo<U>,
U: HasInterner,
[src]Cast a value to type U
using CastTo
.
impl<T> ToOwned for T where
T: Clone,
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impl<T> ToOwned for T where
T: Clone,
[src]type Owned = T
type Owned = T
The resulting type after obtaining ownership.
pub fn to_owned(&self) -> T
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pub fn to_owned(&self) -> T
[src]Creates owned data from borrowed data, usually by cloning. Read more
pub fn clone_into(&self, target: &mut T)
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pub fn clone_into(&self, target: &mut T)
[src]🔬 This is a nightly-only experimental API. (toowned_clone_into
)
recently added
Uses borrowed data to replace owned data, usually by cloning. Read more