# Enum rustc_middle::ty::closure::BorrowKind

source ·

    pub enum BorrowKind {
        ImmBorrow,
        UniqueImmBorrow,
        MutBorrow,
    }

## Variants§

§

### ImmBorrow

Data must be immutable and is aliasable.

§

### UniqueImmBorrow

Data must be immutable but not aliasable. This kind of borrow cannot currently be expressed by the user and is used only in implicit closure bindings. It is needed when the closure is borrowing or mutating a mutable referent, e.g.:

    let mut z = 3;
    let x: &mut isize = &mut z;
    let y = || *x += 5;

If we were to try to translate this closure into a more explicit form, we’d encounter an error with the code as written:

ⓘ

    struct Env<'a> { x: &'a &'a mut isize }
    let mut z = 3;
    let x: &mut isize = &mut z;
    let y = (&mut Env { x: &x }, fn_ptr);  // Closure is pair of env and fn
    fn fn_ptr(env: &mut Env) { **env.x += 5; }

This is then illegal because you cannot mutate a `&mut` found in an aliasable location. To solve, you’d have to translate with an `&mut` borrow:

ⓘ

    struct Env<'a> { x: &'a mut &'a mut isize }
    let mut z = 3;
    let x: &mut isize = &mut z;
    let y = (&mut Env { x: &mut x }, fn_ptr); // changed from &x to &mut x
    fn fn_ptr(env: &mut Env) { **env.x += 5; }

Now the assignment to `**env.x` is legal, but creating a mutable pointer to `x` is not because `x` is not mutable. We could fix this by declaring `x` as `let mut x`. This is ok in user code, if awkward, but extra weird for closures, since the borrow is hidden.

So we introduce a “unique imm” borrow – the referent is immutable, but not aliasable. This solves the problem. For simplicity, we don’t give users the way to express this borrow, it’s just used when translating closures.

FIXME: Rename this to indicate the borrow is actually not immutable.

§

### MutBorrow

Data is mutable and not aliasable.

## Implementations§

source§

### impl BorrowKind

source

#### pub fn from_mutbl(m: Mutability) -> BorrowKind

source

#### pub fn to_mutbl_lossy(self) -> Mutability

Returns a mutability `m` such that an `&m T` pointer could be used to obtain this borrow kind. Because borrow kinds are richer than mutabilities, we sometimes have to pick a mutability that is stronger than necessary so that it at least would permit the borrow in question.

## Trait Implementations§

source§

### impl Clone for BorrowKind

source§

#### fn clone(&self) -> BorrowKind

Returns a copy of the value. Read more
1.0.0 · source§

#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
source§

### impl Debug for BorrowKind

source§

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

Formats the value using the given formatter. Read more
source§

### impl<__D: TyDecoder> Decodable<__D> for BorrowKind

source§

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

source§

### impl<__E: TyEncoder> Encodable<__E> for BorrowKind

source§

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

source§

### impl<'__ctx> HashStable<StableHashingContext<'__ctx>> for BorrowKind

source§

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

source§

### impl PartialEq for BorrowKind

source§

#### fn eq(&self, other: &BorrowKind) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 · source§

#### 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.
source§

### impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for BorrowKind

source§

#### fn try_fold_with<__F: FallibleTypeFolder<TyCtxt<'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
source§

#### fn fold_with<F>(self, folder: &mut F) -> Self
where F: TypeFolder<I>,

A convenient alternative to `try_fold_with` for use with infallible folders. Do not override this method, to ensure coherence with `try_fold_with`.
source§

### impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for BorrowKind

source§

#### fn visit_with<__V: TypeVisitor<TyCtxt<'tcx>>>( &self, __visitor: &mut __V ) -> __V::Result

The entry point for visiting. To visit a value `t` with a visitor `v` call: `t.visit_with(v)`. Read more
source§

### impl Copy for BorrowKind

source§

### impl StructuralPartialEq for BorrowKind

## Auto Trait Implementations§

§

### impl DynSend for BorrowKind

§

### impl DynSync for BorrowKind

§

### impl Freeze for BorrowKind

§

### impl RefUnwindSafe for BorrowKind

§

### impl Send for BorrowKind

§

### impl Sync for BorrowKind

§

### impl Unpin for BorrowKind

§

### impl UnwindSafe for BorrowKind

## Blanket Implementations§

source§

### impl<T> Aligned for T

source§

#### const ALIGN: Alignment = _

Alignment of `Self`.
source§

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

source§

#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
§

### impl<T> AnyEq for T
where T: Any + PartialEq,

§

#### fn equals(&self, other: &(dyn Any + 'static)) -> bool

§

#### fn as_any(&self) -> &(dyn Any + 'static)

source§

### impl<'tcx, T> ArenaAllocatable<'tcx, IsCopy> for T
where T: Copy,

source§

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

source§

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

source§

### impl<'tcx, T> ArenaAllocatable<'tcx, IsCopy> for T
where T: Copy,

source§

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

source§

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

source§

### impl<T> Borrow<T> for T
where T: ?Sized,

source§

#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
source§

### impl<T> BorrowMut<T> for T
where T: ?Sized,

source§

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

Mutably borrows from an owned value. Read more
source§

### impl<T, R> CollectAndApply<T, R> for T

source§

#### 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<_>>())`.

§

#### type Output = R

source§

### impl<Tcx, T> DepNodeParams<Tcx> for T
where Tcx: DepContext, T: for<'a> HashStable<StableHashingContext<'a>> + Debug,

source§

#### default fn fingerprint_style() -> FingerprintStyle

source§

#### 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).
source§

#### default fn to_debug_str(&self, _: Tcx) -> String

source§

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

This method tries to recover the query key from the given `DepNode`, something which is needed when forcing `DepNode`s 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.
§

### impl<T> Filterable for T

§

#### 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
source§

### impl<T> From<T> for T

source§

#### fn from(t: T) -> T

Returns the argument unchanged.

source§

### impl<T> Instrument for T

source§

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

Instruments this type with the provided `Span`, returning an `Instrumented` wrapper. Read more
source§

#### fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current `Span`, returning an `Instrumented` wrapper. Read more
source§

### impl<T, U> Into<U> for T
where U: From<T>,

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.

source§

### impl<P> IntoQueryParam<P> for P

source§

#### fn into_query_param(self) -> P

source§

### impl<'tcx, T> IsSuggestable<'tcx> for T
where T: TypeVisitable<TyCtxt<'tcx>> + TypeFoldable<TyCtxt<'tcx>>,

source§

#### fn is_suggestable(self, tcx: TyCtxt<'tcx>, infer_suggestable: bool) -> bool

Whether this makes sense to suggest in a diagnostic. Read more
source§

#### fn make_suggestable( self, tcx: TyCtxt<'tcx>, infer_suggestable: bool ) -> Option<T>

source§

### impl<T> MaybeResult<T> for T

§

#### type Error = !

source§

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

source§

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

§

### impl<T> Pointable for T

§

#### const ALIGN: usize = _

The alignment of pointer.
§

#### type Init = T

The type for initializers.
§

#### unsafe fn init(init: <T as Pointable>::Init) -> usize

Initializes a with the given initializer. Read more
§

#### unsafe fn deref<'a>(ptr: usize) -> &'a T

Dereferences the given pointer. Read more
§

#### unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut T

Mutably dereferences the given pointer. Read more
§

#### unsafe fn drop(ptr: usize)

Drops the object pointed to by the given pointer. Read more
source§

### impl<T> Same for T

§

#### type Output = T

Should always be `Self`
source§

### impl<T> ToOwned for T
where T: Clone,

§

#### type Owned = T

The resulting type after obtaining ownership.
source§

#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
source§

#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
source§

### impl<'tcx, T> ToPredicate<'tcx, T> for T

source§

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

source§

### impl<T, U> TryFrom<U> for T
where U: Into<T>,

§

#### type Error = Infallible

The type returned in the event of a conversion error.
source§

#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
source§

### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

§

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

The type returned in the event of a conversion error.
source§

#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
source§

### impl<I, T> TypeVisitableExt<I> for T
where I: Interner, T: TypeVisitable<I>,

source§

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

source§

#### 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.
source§

#### fn error_reported(&self) -> Result<(), <I as Interner>::ErrorGuaranteed>

source§

#### 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).
source§

#### 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
source§

#### fn has_projections(&self) -> bool

source§

#### fn has_inherent_projections(&self) -> bool

source§

#### fn has_opaque_types(&self) -> bool

source§

#### fn has_coroutines(&self) -> bool

source§

#### fn references_error(&self) -> bool

source§

#### fn has_non_region_param(&self) -> bool

source§

#### fn has_infer_regions(&self) -> bool

source§

#### fn has_infer_types(&self) -> bool

source§

#### fn has_non_region_infer(&self) -> bool

source§

#### fn has_infer(&self) -> bool

source§

#### fn has_placeholders(&self) -> bool

source§

#### fn has_non_region_placeholders(&self) -> bool

source§

#### fn has_param(&self) -> bool

source§

#### 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.
source§

#### fn has_erased_regions(&self) -> bool

source§

#### fn has_erasable_regions(&self) -> bool

True if there are any un-erased free regions.
source§

#### 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.
source§

#### fn has_bound_regions(&self) -> bool

True if there are any late-bound regions
source§

#### fn has_non_region_bound_vars(&self) -> bool

True if there are any late-bound non-region variables
source§

#### fn has_bound_vars(&self) -> bool

True if there are any bound variables
source§

#### 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.
§

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

§

#### fn vzip(self) -> V

source§

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

source§

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

source§

### impl<T> WithSubscriber for T

source§

#### 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
source§

#### fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default `Subscriber` to this type, returning a `WithDispatch` wrapper. Read more
source§

### impl<'a, T> Captures<'a> for T
where T: ?Sized,

§

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

§

### impl<T> MaybeSendSync for T
where T: Send + Sync,

## Layout§

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain `repr(...)` attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 1 byte

Size for each variant:

- `ImmBorrow`: 0 bytes
- `UniqueImmBorrow`: 0 bytes
- `MutBorrow`: 0 bytes