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) -> String
Trait Implementations
sourceimpl Clone for BorrowKind
impl Clone for BorrowKind
sourcefn clone(&self) -> BorrowKind
fn clone(&self) -> BorrowKind
Returns a copy of the value. Read more
1.0.0 · sourcefn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
Performs copy-assignment from source
. Read more
sourceimpl Debug for BorrowKind
impl Debug for BorrowKind
sourceimpl<'tcx, __D: TyDecoder<'tcx>> Decodable<__D> for BorrowKind
impl<'tcx, __D: TyDecoder<'tcx>> Decodable<__D> for BorrowKind
sourceimpl<'tcx, __E: TyEncoder<'tcx>> Encodable<__E> for BorrowKind
impl<'tcx, __E: TyEncoder<'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 Ord for BorrowKind
impl Ord for BorrowKind
sourceimpl PartialEq<BorrowKind> for BorrowKind
impl PartialEq<BorrowKind> for BorrowKind
sourcefn eq(&self, other: &BorrowKind) -> bool
fn eq(&self, other: &BorrowKind) -> bool
This method tests for self
and other
values to be equal, and is used
by ==
. Read more
sourcefn ne(&self, other: &BorrowKind) -> bool
fn ne(&self, other: &BorrowKind) -> bool
This method tests for !=
.
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>
This method returns an ordering between self
and other
values if one exists. Read more
1.0.0 · sourcefn lt(&self, other: &Rhs) -> bool
fn lt(&self, other: &Rhs) -> bool
This method tests less than (for self
and other
) and is used by the <
operator. Read more
1.0.0 · sourcefn le(&self, other: &Rhs) -> bool
fn le(&self, other: &Rhs) -> bool
This method tests less than or equal to (for self
and other
) and is used by the <=
operator. Read more
impl 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 T where
T: Copy,
impl<'tcx, T> ArenaAllocatable<'tcx, IsCopy> for T where
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 T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more
sourceimpl<Ctxt, T> DepNodeParams<Ctxt> for T where
Ctxt: DepContext,
T: for<'a> HashStable<StableHashingContext<'a>> + Debug,
impl<Ctxt, T> DepNodeParams<Ctxt> for T where
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
This method turns the parameters of a DepNodeConstructor into an opaque Fingerprint to be used in DepNode. Not all DepNodeParams support being turned into a Fingerprint (they don’t need to if the corresponding DepNode is anonymous). Read more
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>
This method tries to recover the query key from the given 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 more
sourceimpl<T> MaybeResult<T> for T
impl<T> MaybeResult<T> for T
sourceimpl<T> ToOwned for T where
T: Clone,
impl<T> ToOwned for T where
T: Clone,
type Owned = T
type Owned = T
The resulting type after obtaining ownership.
sourcefn clone_into(&self, target: &mut T)
fn clone_into(&self, target: &mut T)
toowned_clone_into
)Uses borrowed data to replace owned data, usually by cloning. Read more
impl<'a, T> Captures<'a> for T where
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