[][src]Struct rustc::infer::combine::Generalization

struct Generalization<'tcx> {
    ty: Ty<'tcx>,
    needs_wf: bool,
}
🔬 This is a nightly-only experimental API. (rustc_private)

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Result from a generalization operation. This includes not only the generalized type, but also a bool flag indicating whether further WF checks are needed.

Fields

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

If true, then the generalized type may not be well-formed, even if the source type is well-formed, so we should add an additional check to enforce that it is. This arises in particular around 'bivariant' type parameters that are only constrained by a where-clause. As an example, imagine a type:

struct Foo<A, B> where A: Iterator<Item=B> {
    data: A
}

here, A will be covariant, but B is unconstrained. However, whatever it is, for Foo to be WF, it must be equal to A::Item. If we have an input Foo<?A, ?B>, then after generalization we will wind up with a type like Foo<?C, ?D>. When we enforce that Foo<?A, ?B> <: Foo<?C, ?D> (or >:), we will wind up with the requirement that ?A <: ?C, but no particular relationship between ?B and ?D (after all, we do not know the variance of the normalized form of A::Item with respect to A). If we do nothing else, this may mean that ?D goes unconstrained (as in #41677). So, in this scenario where we create a new type variable in a bivariant context, we set the needs_wf flag to true. This will force the calling code to check that WF(Foo<?C, ?D>) holds, which in turn implies that ?C::Item == ?D. So once ?C is constrained, that should suffice to restrict ?D.

Auto Trait Implementations

impl<'tcx> !Send for Generalization<'tcx>

impl<'tcx> !Sync for Generalization<'tcx>

Blanket Implementations

impl<T> MaybeResult for T
[src]

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

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

impl<T> From for T
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Performs the conversion.

impl<T, U> Into for T where
    U: From<T>, 
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Performs the conversion.

impl<T, U> TryFrom for T where
    T: From<U>, 
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🔬 This is a nightly-only experimental API. (try_from)

The type returned in the event of a conversion error.

🔬 This is a nightly-only experimental API. (try_from)

Performs the conversion.

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

Important traits for &'a mut R

Immutably borrows from an owned value. Read more

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

🔬 This is a nightly-only experimental API. (try_from)

The type returned in the event of a conversion error.

🔬 This is a nightly-only experimental API. (try_from)

Performs the conversion.

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

Important traits for &'a mut R

Mutably borrows from an owned value. Read more

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

🔬 This is a nightly-only experimental API. (get_type_id)

this method will likely be replaced by an associated static

Gets the TypeId of self. Read more

impl<E> SpecializationError for E
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🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

Create an error for a missing method specialization. Defaults to panicking with type, trait & method names. S is the encoder/decoder state type, T is the type being encoded/decoded, and the arguments are the names of the trait and method that should've been overridden. Read more

impl<T> Erased for T
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impl<T> Send for T where
    T: ?Sized
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impl<T> Sync for T where
    T: ?Sized
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impl<T> Erased for T