Enum rustc_middle::mir::BorrowKind
source · 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
sourceimpl BorrowKind
impl BorrowKind
pub fn to_mutbl_lossy(self) -> Mutability
sourceimpl BorrowKind
impl BorrowKind
pub fn allows_two_phase_borrow(&self) -> bool
pub fn describe_mutability(&self) -> &str
Trait Implementations
sourceimpl Clone for BorrowKind
impl Clone for BorrowKind
sourcefn clone(&self) -> BorrowKind
fn clone(&self) -> BorrowKind
1.0.0 · sourcefn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read moresourceimpl Debug for BorrowKind
impl Debug for BorrowKind
sourceimpl<'tcx, __D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<__D> for BorrowKind
impl<'tcx, __D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<__D> for BorrowKind
sourceimpl<'tcx, __E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<__E> for BorrowKind
impl<'tcx, __E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<__E> for BorrowKind
sourceimpl Hash for BorrowKind
impl Hash for BorrowKind
sourceimpl<'__ctx> HashStable<StableHashingContext<'__ctx>> for BorrowKind
impl<'__ctx> HashStable<StableHashingContext<'__ctx>> for BorrowKind
fn hash_stable(
&self,
__hcx: &mut StableHashingContext<'__ctx>,
__hasher: &mut StableHasher
)
sourceimpl<'tcx> Lift<'tcx> for BorrowKind
impl<'tcx> Lift<'tcx> for BorrowKind
type Lifted = BorrowKind
fn lift_to_tcx(self, _: TyCtxt<'tcx>) -> Option<Self>
sourceimpl Ord for BorrowKind
impl Ord for BorrowKind
sourcefn cmp(&self, other: &BorrowKind) -> Ordering
fn cmp(&self, other: &BorrowKind) -> Ordering
1.21.0 · sourcefn max(self, other: Self) -> Self
fn max(self, other: Self) -> Self
1.21.0 · sourcefn min(self, other: Self) -> Self
fn min(self, other: Self) -> Self
1.50.0 · sourcefn clamp(self, min: Self, max: Self) -> Selfwhere
Self: PartialOrd<Self>,
fn clamp(self, min: Self, max: Self) -> Selfwhere
Self: PartialOrd<Self>,
sourceimpl PartialEq<BorrowKind> for BorrowKind
impl PartialEq<BorrowKind> for BorrowKind
sourcefn eq(&self, other: &BorrowKind) -> bool
fn eq(&self, other: &BorrowKind) -> bool
sourceimpl PartialOrd<BorrowKind> for BorrowKind
impl PartialOrd<BorrowKind> for BorrowKind
sourcefn partial_cmp(&self, other: &BorrowKind) -> Option<Ordering>
fn partial_cmp(&self, other: &BorrowKind) -> Option<Ordering>
1.0.0 · sourcefn le(&self, other: &Rhs) -> bool
fn le(&self, other: &Rhs) -> bool
self
and other
) and is used by the <=
operator. Read moresourceimpl<'tcx> TypeFoldable<'tcx> for BorrowKind
impl<'tcx> TypeFoldable<'tcx> for BorrowKind
sourcefn try_fold_with<F: FallibleTypeFolder<'tcx>>(
self,
_: &mut F
) -> Result<BorrowKind, F::Error>
fn try_fold_with<F: FallibleTypeFolder<'tcx>>(
self,
_: &mut F
) -> Result<BorrowKind, F::Error>
sourcefn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self
fn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self
try_fold_with
for use with infallible
folders. Do not override this method, to ensure coherence with
try_fold_with
. Read moresourceimpl<'tcx> TypeVisitable<'tcx> for BorrowKind
impl<'tcx> TypeVisitable<'tcx> for BorrowKind
sourcefn visit_with<F: TypeVisitor<'tcx>>(&self, _: &mut F) -> ControlFlow<F::BreakTy>
fn visit_with<F: TypeVisitor<'tcx>>(&self, _: &mut F) -> ControlFlow<F::BreakTy>
sourcefn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool
fn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool
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. Read moresourcefn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool
fn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool
true
if this self
has any regions that escape binder
(and
hence are not bound by it). Read morefn 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
sourcefn has_free_regions(&self) -> bool
fn has_free_regions(&self) -> bool
fn has_erased_regions(&self) -> bool
sourcefn has_erasable_regions(&self) -> bool
fn has_erasable_regions(&self) -> bool
sourcefn is_global(&self) -> bool
fn is_global(&self) -> bool
sourcefn has_late_bound_regions(&self) -> bool
fn has_late_bound_regions(&self) -> bool
sourcefn still_further_specializable(&self) -> bool
fn still_further_specializable(&self) -> bool
impl
specialization. Read moreimpl Copy for BorrowKind
impl Eq for BorrowKind
impl StructuralEq for BorrowKind
impl StructuralPartialEq for BorrowKind
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
sourceimpl<'tcx, T> ArenaAllocatable<'tcx, IsCopy> for Twhere
T: Copy,
impl<'tcx, T> ArenaAllocatable<'tcx, IsCopy> for Twhere
T: Copy,
fn allocate_on(self, arena: &'a Arena<'tcx>) -> &'a mut T
fn allocate_from_iter(
arena: &'a Arena<'tcx>,
iter: impl IntoIterator<Item = T>
) -> &'a mut [T]ⓘNotable traits for &[u8]impl Read for &[u8]impl Write for &mut [u8]
sourceimpl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
sourceimpl<Ctxt, T> DepNodeParams<Ctxt> for Twhere
Ctxt: DepContext,
T: for<'a> HashStable<StableHashingContext<'a>> + Debug,
impl<Ctxt, T> DepNodeParams<Ctxt> for Twhere
Ctxt: DepContext,
T: for<'a> HashStable<StableHashingContext<'a>> + Debug,
default fn fingerprint_style() -> FingerprintStyle
sourcedefault fn to_fingerprint(&self, tcx: Ctxt) -> Fingerprint
default fn to_fingerprint(&self, tcx: Ctxt) -> Fingerprint
default fn to_debug_str(&self, Ctxt) -> String
sourcedefault fn recover(Ctxt, &DepNode<<Ctxt as DepContext>::DepKind>) -> Option<T>
default fn recover(Ctxt, &DepNode<<Ctxt as DepContext>::DepKind>) -> Option<T>
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. Read moresourceimpl<T, R> InternIteratorElement<T, R> for T
impl<T, R> InternIteratorElement<T, R> for T
type Output = R
fn intern_with<I, F>(iter: I, f: F) -> <T as InternIteratorElement<T, R>>::Outputwhere
I: Iterator<Item = T>,
F: FnOnce(&[T]) -> R,
sourceimpl<T> MaybeResult<T> for T
impl<T> MaybeResult<T> for T
sourceimpl<CTX, T> Value<CTX> for Twhere
CTX: DepContext,
impl<CTX, T> Value<CTX> for Twhere
CTX: DepContext,
default fn from_cycle_error(tcx: CTX) -> T
impl<'a, T> Captures<'a> for Twhere
T: ?Sized,
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 bytesShallow
: 0 bytesUnique
: 0 bytesMut
: 1 byte