Enum rustc_middle::mir::syntax::BorrowKind

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

Variants

Shared

Data must be immutable and is aliasable.

Shallow

The immediately borrowed place must be immutable, but projections from it don’t need to be. For example, a shallow borrow of a.b doesn’t conflict with a mutable borrow of a.b.c.

This is used when lowering matches: when matching on a place we want to ensure that place have the same value from the start of the match until an arm is selected. This prevents this code from compiling:

let mut x = &Some(0);
match *x {
    None => (),
    Some(_) if { x = &None; false } => (),
    Some(_) => (),
}

This can’t be a shared borrow because mutably borrowing (*x as Some).0 should not prevent if let None = x { ... }, for example, because the mutating (*x as Some).0 can’t affect the discriminant of x. We can also report errors with this kind of borrow differently.

Unique

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 an &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.

Mut

Fields

allow_two_phase_borrow: bool

true if this borrow arose from method-call auto-ref (i.e., adjustment::Adjust::Borrow).

Data is mutable and not aliasable.

Implementations

impl BorrowKind

pub fn to_mutbl_lossy(self) -> Mutability

impl BorrowKind

pub fn allows_two_phase_borrow(&self) -> bool

pub fn describe_mutability(&self) -> &str

Trait Implementations

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<'tcx, __D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<__D> for BorrowKind

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

impl<'tcx, __E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<__E> for BorrowKind

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

impl Hash for BorrowKind

fn hash<__H: Hasher>(&self, state: &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<'__ctx> HashStable<StableHashingContext<'__ctx>> for BorrowKind

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

impl<'tcx> Lift<'tcx> for BorrowKind

type Lifted = BorrowKind

fn lift_to_tcx(self, _: TyCtxt<'tcx>) -> Option<Self>

impl Ord for BorrowKind

fn cmp(&self, other: &BorrowKind) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Selfwhere
    Self: PartialOrd<Self>,

Restrict a value to a certain interval.

impl PartialEq<BorrowKind> 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: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd<BorrowKind> for BorrowKind

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

This method returns an ordering between self and other values if one exists.

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

This method tests less than (for self and other) and is used by the < operator.

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

This method tests less than or equal to (for self and other) and is used by the <= operator.

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

This method tests greater than (for self and other) and is used by the > operator.

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

This method tests greater than or equal to (for self and other) and is used by the >= operator.

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

fn try_fold_with<F: FallibleTypeFolder<'tcx>>(
    self,
    _: &mut F
) -> Result<BorrowKind, F::Error>

The entry point for folding. To fold a value t with a folder f call: t.try_fold_with(f).

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.

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

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

The entry point for visiting. To visit a value t with a visitor v call: t.visit_with(v).

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.

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

Returns true if this self has any regions that escape binder (and hence are not bound by it).

fn has_escaping_bound_vars(&self) -> bool

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

fn has_projections(&self) -> bool

fn has_opaque_types(&self) -> bool

fn references_error(&self) -> bool

fn error_reported(&self) -> Option<ErrorGuaranteed>

fn has_param_types_or_consts(&self) -> bool

fn has_infer_regions(&self) -> bool

fn has_infer_types(&self) -> bool

fn has_infer_types_or_consts(&self) -> bool

fn needs_infer(&self) -> bool

fn has_placeholders(&self) -> bool

fn needs_subst(&self) -> bool

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.

fn has_erased_regions(&self) -> bool

fn has_erasable_regions(&self) -> bool

True if there are any un-erased free regions.

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.

fn has_late_bound_regions(&self) -> bool

True if there are any late-bound regions

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 Copy for BorrowKind

impl Eq for BorrowKind

impl StructuralEq for BorrowKind

impl StructuralPartialEq for BorrowKind

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:

• Shared: 0 bytes
• Shallow: 0 bytes
• Unique: 0 bytes
• Mut: 1 byte