[][src]Enum rustc::ty::Variance

pub enum Variance {
    Covariant,
    Invariant,
    Contravariant,
    Bivariant,
}
⚙️ This is an internal compiler API. (rustc_private)

This crate is being loaded from the sysroot, a permanently unstable location for private compiler dependencies. It is not intended for general use. Prefer using a public version of this crate from crates.io via Cargo.toml.

Variants

Covariant
⚙️ This is an internal compiler API. (rustc_private)

This crate is being loaded from the sysroot, a permanently unstable location for private compiler dependencies. It is not intended for general use. Prefer using a public version of this crate from crates.io via Cargo.toml.

Invariant
⚙️ This is an internal compiler API. (rustc_private)

This crate is being loaded from the sysroot, a permanently unstable location for private compiler dependencies. It is not intended for general use. Prefer using a public version of this crate from crates.io via Cargo.toml.

Contravariant
⚙️ This is an internal compiler API. (rustc_private)

This crate is being loaded from the sysroot, a permanently unstable location for private compiler dependencies. It is not intended for general use. Prefer using a public version of this crate from crates.io via Cargo.toml.

Bivariant
⚙️ This is an internal compiler API. (rustc_private)

This crate is being loaded from the sysroot, a permanently unstable location for private compiler dependencies. It is not intended for general use. Prefer using a public version of this crate from crates.io via Cargo.toml.

Methods

impl Variance[src]

pub fn xform(self, v: Variance) -> Variance[src]

⚙️ This is an internal compiler API. (rustc_private)

This crate is being loaded from the sysroot, a permanently unstable location for private compiler dependencies. It is not intended for general use. Prefer using a public version of this crate from crates.io via Cargo.toml.

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

impl Clone for Variance[src]

impl Copy for Variance[src]

impl Debug for Variance[src]

impl Decodable for Variance[src]

impl Encodable for Variance[src]

impl<'__ctx> HashStable<StableHashingContext<'__ctx>> for Variance[src]

impl<'tcx> Lift<'tcx> for Variance[src]

type Lifted = Self

⚙️ This is an internal compiler API. (rustc_private)

This crate is being loaded from the sysroot, a permanently unstable location for private compiler dependencies. It is not intended for general use. Prefer using a public version of this crate from crates.io via Cargo.toml.

impl PartialEq<Variance> for Variance[src]

impl StructuralPartialEq for Variance[src]

impl<'tcx> TypeFoldable<'tcx> for Variance[src]

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> Any for T where
    T: 'static + ?Sized
[src]

impl<T> ArenaAllocatable for T where
    T: Copy
[src]

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

impl<'a, T> Captures<'a> for T where
    T: ?Sized
[src]

impl<T> Decodable for T where
    T: UseSpecializedDecodable
[src]

impl<T> Encodable for T where
    T: UseSpecializedEncodable + ?Sized
[src]

impl<T> Erased for T[src]

impl<T> From<T> for T[src]

impl<T, U> Into<U> for T where
    U: From<T>, 
[src]

impl<T> MaybeResult<T> for T[src]

type Error = !

⚙️ This is an internal compiler API. (rustc_private)

This crate is being loaded from the sysroot, a permanently unstable location for private compiler dependencies. It is not intended for general use. Prefer using a public version of this crate from crates.io via Cargo.toml.

impl<E> SpecializationError for E[src]

impl<'tcx, T> Subst<'tcx> for T where
    T: TypeFoldable<'tcx>, 
[src]

impl<T> ToOwned for T where
    T: Clone
[src]

type Owned = T

The resulting type after obtaining ownership.

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

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

The type returned in the event of a conversion error.