pub struct WithOptConstParam<T> {
    pub did: T,
    pub const_param_did: Option<DefId>,
}
Expand description

A DefId which, in case it is a const argument, is potentially bundled with the DefId of the generic parameter it instantiates.

This is used to avoid calls to type_of for const arguments during typeck which cause cycle errors.

struct A;
impl A {
    fn foo<const N: usize>(&self) -> [u8; N] { [0; N] }
    //           ^ const parameter
}
struct B;
impl B {
    fn foo<const M: u8>(&self) -> usize { 42 }
    //           ^ const parameter
}

fn main() {
    let a = A;
    let _b = a.foo::<{ 3 + 7 }>();
    //               ^^^^^^^^^ const argument
}

Let’s look at the call a.foo::<{ 3 + 7 }>() here. We do not know which foo is used until we know the type of a.

We only know the type of a once we are inside of typeck(main). We also end up normalizing the type of _b during typeck(main) which requires us to evaluate the const argument.

To evaluate that const argument we need to know its type, which we would get using type_of(const_arg). This requires us to resolve foo as it can be either usize or u8 in this example. However, resolving foo once again requires typeck(main) to get the type of a, which results in a cycle.

In short we must not call type_of(const_arg) during typeck(main).

When first creating the ty::Const of the const argument inside of typeck we have already resolved foo so we know which const parameter this argument instantiates. This means that we also know the expected result of type_of(const_arg) even if we aren’t allowed to call that query: it is equal to type_of(const_param) which is trivial to compute.

If we now want to use that constant in a place which potentially needs its type we also pass the type of its const_param. This is the point of WithOptConstParam, except that instead of a Ty we bundle the DefId of the const parameter. Meaning that we need to use type_of(const_param_did) if const_param_did is Some to get the type of did.

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§did: T§const_param_did: Option<DefId>

The DefId of the corresponding generic parameter in case did is a const argument.

Note that even if did is a const argument, this may still be None. All queries taking WithOptConstParam start by calling tcx.opt_const_param_of(def.did) to potentially update param_did in the case it is None.

Implementations§

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impl<T> WithOptConstParam<T>

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pub fn unknown(did: T) -> WithOptConstParam<T>

Creates a new WithOptConstParam setting const_param_did to None.

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impl WithOptConstParam<LocalDefId>

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pub fn try_lookup(
    did: LocalDefId,
    tcx: TyCtxt<'_>
) -> Option<(LocalDefId, DefId)>

Returns Some((did, param_did)) if def_id is a const argument, None otherwise.

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pub fn try_upgrade(
    self,
    tcx: TyCtxt<'_>
) -> Option<WithOptConstParam<LocalDefId>>

In case self is unknown but self.did is a const argument, this returns a WithOptConstParam with the correct const_param_did.

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pub fn to_global(self) -> WithOptConstParam<DefId>

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pub fn def_id_for_type_of(self) -> DefId

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impl WithOptConstParam<DefId>

Trait Implementations§

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impl<T: Clone> Clone for WithOptConstParam<T>

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fn clone(&self) -> WithOptConstParam<T>

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl<T: Debug> Debug for WithOptConstParam<T>

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

Formats the value using the given formatter. Read more
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impl<'tcx, T, __D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<__D> for WithOptConstParam<T>where
    T: Decodable<__D>,

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fn decode(__decoder: &mut __D) -> Self

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impl<'tcx, T, __E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<__E> for WithOptConstParam<T>where
    T: Encodable<__E>,

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fn encode(&self, __encoder: &mut __E)

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impl<T: Hash> Hash for WithOptConstParam<T>

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fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher. Read more
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fn hash_slice<H>(data: &[Self], state: &mut H)where
    H: Hasher,
    Self: Sized,

Feeds a slice of this type into the given Hasher. Read more
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impl<'__ctx, T> HashStable<StableHashingContext<'__ctx>> for WithOptConstParam<T>where
    T: HashStable<StableHashingContext<'__ctx>>,

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fn hash_stable(
    &self,
    __hcx: &mut StableHashingContext<'__ctx>,
    __hasher: &mut StableHasher
)

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impl Key for WithOptConstParam<LocalDefId>

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type CacheSelector = DefaultCacheSelector<WithOptConstParam<LocalDefId>>

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fn query_crate_is_local(&self) -> bool

Given an instance of this key, what crate is it referring to? This is used to find the provider.
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fn default_span(&self, tcx: TyCtxt<'_>) -> Span

In the event that a cycle occurs, if no explicit span has been given for a query with key self, what span should we use?
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fn key_as_def_id(&self) -> Option<DefId>

If the key is a DefId or DefId–equivalent, return that DefId. Otherwise, return None.
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fn ty_adt_id(&self) -> Option<DefId>

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impl<'__lifted, T> Lift<'__lifted> for WithOptConstParam<T>where
    T: Lift<'__lifted>,

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type Lifted = WithOptConstParam<<T as Lift<'__lifted>>::Lifted>

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fn lift_to_tcx(
    self,
    __tcx: TyCtxt<'__lifted>
) -> Option<WithOptConstParam<T::Lifted>>

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impl<T: Ord> Ord for WithOptConstParam<T>

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fn cmp(&self, other: &WithOptConstParam<T>) -> Ordering

This method returns an Ordering between self and other. Read more
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fn max(self, other: Self) -> Selfwhere
    Self: Sized,

Compares and returns the maximum of two values. Read more
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fn min(self, other: Self) -> Selfwhere
    Self: Sized,

Compares and returns the minimum of two values. Read more
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fn clamp(self, min: Self, max: Self) -> Selfwhere
    Self: Sized + PartialOrd<Self>,

Restrict a value to a certain interval. Read more
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impl<T: PartialEq> PartialEq<WithOptConstParam<T>> for WithOptConstParam<T>

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fn eq(&self, other: &WithOptConstParam<T>) -> bool

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl<T: PartialOrd> PartialOrd<WithOptConstParam<T>> for WithOptConstParam<T>

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fn partial_cmp(&self, other: &WithOptConstParam<T>) -> Option<Ordering>

This method returns an ordering between self and other values if one exists. Read more
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fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator. Read more
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fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more
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fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator. Read more
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fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more
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impl<'tcx, T> TypeFoldable<'tcx> for WithOptConstParam<T>where
    T: TypeFoldable<'tcx>,

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fn try_fold_with<__F: FallibleTypeFolder<'tcx>>(
    self,
    __folder: &mut __F
) -> Result<Self, __F::Error>

The entry point for folding. To fold a value t with a folder f call: t.try_fold_with(f). Read more
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fn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self

A convenient alternative to try_fold_with for use with infallible folders. Do not override this method, to ensure coherence with try_fold_with.
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impl<'tcx, T> TypeVisitable<'tcx> for WithOptConstParam<T>where
    T: TypeVisitable<'tcx>,

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fn visit_with<__V: TypeVisitor<'tcx>>(
    &self,
    __visitor: &mut __V
) -> ControlFlow<__V::BreakTy>

The entry point for visiting. To visit a value t with a visitor v call: t.visit_with(v). Read more
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fn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool

Returns 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.
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fn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool

Returns true if this type has any regions that escape binder (and hence are not bound by it).
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fn has_escaping_bound_vars(&self) -> bool

Return 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 more
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fn has_type_flags(&self, flags: TypeFlags) -> bool

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fn has_projections(&self) -> bool

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fn has_opaque_types(&self) -> bool

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fn has_generators(&self) -> bool

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fn references_error(&self) -> bool

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fn error_reported(&self) -> Result<(), ErrorGuaranteed>

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fn has_non_region_param(&self) -> bool

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fn has_infer_regions(&self) -> bool

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fn has_infer_types(&self) -> bool

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fn has_non_region_infer(&self) -> bool

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fn needs_infer(&self) -> bool

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fn has_placeholders(&self) -> bool

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fn needs_subst(&self) -> bool

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fn has_free_regions(&self) -> bool

“Free” regions in this context means that it has any region that is not (a) erased or (b) late-bound.
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fn has_erased_regions(&self) -> bool

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fn has_erasable_regions(&self) -> bool

True if there are any un-erased free regions.
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fn is_global(&self) -> bool

Indicates whether this value references only ‘global’ generic parameters that are the same regardless of what fn we are in. This is used for caching.
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fn has_late_bound_regions(&self) -> bool

True if there are any late-bound regions
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fn has_non_region_late_bound(&self) -> bool

True if there are any late-bound non-region variables
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fn has_late_bound_vars(&self) -> bool

True if there are any late-bound variables
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fn still_further_specializable(&self) -> bool

Indicates whether this value still has parameters/placeholders/inference variables which could be replaced later, in a way that would change the results of impl specialization.
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impl<T: Copy> Copy for WithOptConstParam<T>

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impl<T: Eq> Eq for WithOptConstParam<T>

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impl<T> StructuralEq for WithOptConstParam<T>

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impl<T> StructuralPartialEq for WithOptConstParam<T>

Auto Trait Implementations§

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

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

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

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

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

Blanket Implementations§

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impl<T> Any for Twhere
    T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<'tcx, T> ArenaAllocatable<'tcx, IsCopy> for Twhere
    T: Copy,

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fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut T

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fn allocate_from_iter<'a>(
    arena: &'a Arena<'tcx>,
    iter: impl IntoIterator<Item = T>
) -> &'a mut [T]

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impl<T> Borrow<T> for Twhere
    T: ?Sized,

const: unstable · source§

fn borrow(&self) -> &T

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

const: unstable · source§

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

Mutably borrows from an owned value. Read more
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impl<Tcx, T> DepNodeParams<Tcx> for Twhere
    Tcx: DepContext,
    T: for<'a> HashStable<StableHashingContext<'a>> + Debug,

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default fn fingerprint_style() -> FingerprintStyle

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default fn to_fingerprint(&self, tcx: Tcx) -> Fingerprint

This method turns the parameters of a DepNodeConstructor into an opaque Fingerprint to be used in DepNode. Not all DepNodeParams support being turned into a Fingerprint (they don’t need to if the corresponding DepNode is anonymous).
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default fn to_debug_str(&self, _: Tcx) -> String

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default fn recover(
    _: Tcx,
    _: &DepNode<<Tcx as DepContext>::DepKind>
) -> Option<T>

This method tries to recover the query key from the given DepNode, something which is needed when forcing DepNodes during red-green evaluation. The query system will only call this method if fingerprint_style() is not FingerprintStyle::Opaque. It is always valid to return None here, in which case incremental compilation will treat the query as having changed instead of forcing it.
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impl<T> From<T> for T

const: unstable · source§

fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, R> InternIteratorElement<T, R> for T

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type Output = R

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fn intern_with<I, F>(iter: I, f: F) -> <T as InternIteratorElement<T, R>>::Outputwhere
    I: Iterator<Item = T>,
    F: FnOnce(&[T]) -> R,

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impl<T, U> Into<U> for Twhere
    U: From<T>,

const: unstable · source§

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> 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> ToOwned for Twhere
    T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<'tcx, T> ToPredicate<'tcx, T> for T

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fn to_predicate(self, _tcx: TyCtxt<'tcx>) -> T

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impl<T, U> TryFrom<U> for Twhere
    U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
const: unstable · source§

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 Twhere
    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<Tcx, T, D> Value<Tcx, D> for Twhere
    Tcx: DepContext,
    D: DepKind,

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default fn from_cycle_error(tcx: Tcx, _: &[QueryInfo<D>]) -> 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.