Enum rustc::mir::BorrowKind

pub enum BorrowKind {
    Shared,
    Unique,
    Mut {
        allow_two_phase_borrow: bool,
    },
}

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Variants

Shared

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Data must be immutable and is aliasable.

Unique

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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 you 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.

Mut

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Data is mutable and not aliasable.

Fields of Mut

allow_two_phase_borrow: bool

🔬 This is a nightly-only experimental API. (rustc_private) this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead? True if this borrow arose from method-call auto-ref (i.e. adjustment::Adjust::Borrow)

Methods

impl BorrowKind

pub fn to_mutbl_lossy(self) -> Mutability

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impl BorrowKind

pub fn allows_two_phase_borrow(&self) -> bool

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Trait Implementations

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

fn hash_stable<W: StableHasherResult>(     &self,     hcx: &mut StableHashingContext<'a>,     hasher: &mut StableHasher<W> )

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impl Copy for BorrowKind

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 Debug for BorrowKind

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

Formats the value using the given formatter.

impl PartialEq for BorrowKind

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

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

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

This method tests for !=.

impl Eq for BorrowKind

fn assert_receiver_is_total_eq(&self)

impl Encodable for BorrowKind

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

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impl Decodable for BorrowKind

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

🔬 This is a nightly-only experimental API. (rustc_private)

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