Enum rustc::ty::BorrowKind

pub enum BorrowKind {
    ImmBorrow,
    UniqueImmBorrow,
    MutBorrow,
}

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Variants

ImmBorrow

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Data must be immutable and is aliasable.

UniqueImmBorrow

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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.

MutBorrow

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Data is mutable and not aliasable.

Methods

impl BorrowKind

pub fn from_mutbl(m: Mutability) -> BorrowKind

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pub fn to_mutbl_lossy(self) -> Mutability

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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.

pub fn to_user_str(&self) -> &'static str

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Trait Implementations

impl<'tcx> HashStable<StableHashingContext<'tcx>> for BorrowKind

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

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impl Clone for BorrowKind

fn clone(&self) -> BorrowKind

Returns a copy of the value.

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

Performs copy-assignment from source.

impl PartialEq for BorrowKind

fn eq(&self, __arg_0: &BorrowKind) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl Eq for BorrowKind

impl Hash for BorrowKind

fn hash<__H: Hasher>(&self, __arg_0: &mut __H)

Feeds this value into the given [Hasher].

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given [Hasher].

impl Debug for BorrowKind

fn fmt(&self, __arg_0: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Encodable for BorrowKind

fn encode<__S: Encoder>(&self, __arg_0: &mut __S) -> Result<(), __S::Error>

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impl Decodable for BorrowKind

fn decode<__D: Decoder>(__arg_0: &mut __D) -> Result<BorrowKind, __D::Error>

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impl Copy for BorrowKind