Struct rustc_infer::infer::relate::generalize::Generalization

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struct Generalization<T> {
    pub value_may_be_infer: T,
    pub has_unconstrained_ty_var: bool,
}
Expand description

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

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§value_may_be_infer: T

When generalizing <?0 as Trait>::Assoc or <T as Bar<<?0 as Foo>::Assoc>>::Assoc for ?0 generalization returns an inference variable.

This has to be handled wotj care as it can otherwise very easily result in infinite recursion.

§has_unconstrained_ty_var: bool

In general, we do not check whether all types which occur during type checking are well-formed. We only check wf of user-provided types and when actually using a type, e.g. for method calls.

This means that when subtyping, we may end up with unconstrained inference variables if a generalized type has bivariant parameters. A parameter may only be bivariant if it is constrained by a projection bound in 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 Foo<?A, ?B> <: Foo<?C, ?D>, we will wind up with the requirement that ?A <: ?C, but no particular relationship between ?B and ?D (after all, these types may be completely different). If we do nothing else, this may mean that ?D goes unconstrained (as in #41677). To avoid this we emit a WellFormed obligation in these cases.

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impl<T: Debug> Debug for Generalization<T>

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more

Auto Trait Implementations§

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impl<T> Freeze for Generalization<T>
where T: Freeze,

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impl<T> RefUnwindSafe for Generalization<T>
where T: RefUnwindSafe,

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impl<T> Send for Generalization<T>
where T: Send,

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impl<T> Sync for Generalization<T>
where T: Sync,

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impl<T> Unpin for Generalization<T>
where T: Unpin,

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impl<T> UnwindSafe for Generalization<T>
where T: UnwindSafe,

Blanket Implementations§

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impl<T> Aligned for T

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const ALIGN: Alignment = _

Alignment of Self.
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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T, R> CollectAndApply<T, R> for T

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fn collect_and_apply<I, F>(iter: I, f: F) -> R
where I: Iterator<Item = T>, F: FnOnce(&[T]) -> R,

Equivalent to f(&iter.collect::<Vec<_>>()).

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type Output = R

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impl<T> Filterable for T

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fn filterable( self, filter_name: &'static str, ) -> RequestFilterDataProvider<T, fn(_: DataRequest<'_>) -> bool>

Creates a filterable data provider with the given name for debugging. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T> Instrument for T

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fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
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fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current Span, returning an Instrumented wrapper. Read more
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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> IntoEither for T

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fn into_either(self, into_left: bool) -> Either<Self, Self>

Converts 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 more
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fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
where F: FnOnce(&Self) -> bool,

Converts 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 more
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impl<P> IntoQueryParam<P> for P

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impl<T> MaybeResult<T> for T

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type Error = !

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fn from(_: Result<T, <T as MaybeResult<T>>::Error>) -> T

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fn to_result(self) -> Result<T, <T as MaybeResult<T>>::Error>

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impl<T> Same for T

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type Output = T

Should always be Self
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<I, T, U> Upcast<I, U> for T
where U: UpcastFrom<I, T>,

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fn upcast(self, interner: I) -> U

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impl<I, T> UpcastFrom<I, T> for T

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fn upcast_from(from: T, _tcx: I) -> T

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impl<V, T> VZip<V> for T
where V: MultiLane<T>,

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fn vzip(self) -> V

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impl<Tcx, T> Value<Tcx> for T
where Tcx: DepContext,

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default fn from_cycle_error( tcx: Tcx, cycle_error: &CycleError, _guar: ErrorGuaranteed, ) -> T

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impl<T> WithSubscriber for T

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fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
where S: Into<Dispatch>,

Attaches the provided Subscriber to this type, returning a WithDispatch wrapper. Read more
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fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default Subscriber to this type, returning a WithDispatch wrapper. Read more
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impl<'a, T> Captures<'a> for T
where T: ?Sized,

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impl<T> ErasedDestructor for T
where T: 'static,

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impl<T> MaybeSendSync for T

Layout§

Note: Unable to compute type layout, possibly due to this type having generic parameters. Layout can only be computed for concrete, fully-instantiated types.