Enum rustc_middle::ty::BorrowKind[][src]

pub enum BorrowKind {



Data must be immutable and is aliasable.


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 x: &mut isize = ...;
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 { x: & &mut isize }
let x: &mut isize = ...;
let y = (&mut Env { &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 { x: & &mut isize }
let x: &mut isize = ...;
let y = (&mut Env { &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.


Data is mutable and not aliasable.


impl BorrowKind[src]

pub fn from_mutbl(m: Mutability) -> BorrowKind[src]

pub fn to_mutbl_lossy(self) -> Mutability[src]

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

impl Clone for BorrowKind[src]

impl Copy for BorrowKind[src]

impl Debug for BorrowKind[src]

impl<'tcx, __D: TyDecoder<'tcx>> Decodable<__D> for BorrowKind[src]

impl<'tcx, __E: TyEncoder<'tcx>> Encodable<__E> for BorrowKind[src]

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

impl PartialEq<BorrowKind> for BorrowKind[src]

impl StructuralPartialEq for BorrowKind[src]

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

Auto Trait Implementations

impl RefUnwindSafe for BorrowKind

impl Send for BorrowKind

impl Sync for BorrowKind

impl Unpin for BorrowKind

impl UnwindSafe for BorrowKind

Blanket Implementations

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

impl<'tcx, T> ArenaAllocatable<'tcx, ()> for T where
    T: Copy

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

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

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

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

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

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

type Error = !

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

impl<T> ToOwned for T where
    T: Clone

type Owned = T

The resulting type after obtaining ownership.

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

type Error = Infallible

The type returned in the event of a conversion error.

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.

impl<T> WithConstness for T[src]