pub enum FakeReadCause {
ForMatchGuard,
ForMatchedPlace(Option<LocalDefId>),
ForGuardBinding,
ForLet(Option<LocalDefId>),
ForIndex,
}
Expand description
The FakeReadCause
describes the type of pattern why a FakeRead statement exists.
Variants§
ForMatchGuard
Inject a fake read of the borrowed input at the end of each guards code.
This should ensure that you cannot change the variant for an enum while you are in the midst of matching on it.
ForMatchedPlace(Option<LocalDefId>)
let x: !; match x {}
doesn’t generate any read of x so we need to
generate a read of x to check that it is initialized and safe.
If a closure pattern matches a Place starting with an Upvar, then we introduce a FakeRead for that Place outside the closure, in such a case this option would be Some(closure_def_id). Otherwise, the value of the optional LocalDefId will be None.
ForGuardBinding
A fake read of the RefWithinGuard version of a bind-by-value variable in a match guard to ensure that its value hasn’t change by the time we create the OutsideGuard version.
ForLet(Option<LocalDefId>)
Officially, the semantics of
let pattern = <expr>;
is that <expr>
is evaluated into a temporary and then this temporary is
into the pattern.
However, if we see the simple pattern let var = <expr>
, we optimize this to
evaluate <expr>
directly into the variable var
. This is mostly unobservable,
but in some cases it can affect the borrow checker, as in #53695.
Therefore, we insert a “fake read” here to ensure that we get
appropriate errors.
If a closure pattern matches a Place starting with an Upvar, then we introduce a FakeRead for that Place outside the closure, in such a case this option would be Some(closure_def_id). Otherwise, the value of the optional DefId will be None.
ForIndex
If we have an index expression like
(*x)[1][{ x = y; 4}]
then the first bounds check is invalidated when we evaluate the second
index expression. Thus we create a fake borrow of x
across the second
indexer, which will cause a borrow check error.
Trait Implementations§
Source§impl Clone for FakeReadCause
impl Clone for FakeReadCause
Source§fn clone(&self) -> FakeReadCause
fn clone(&self) -> FakeReadCause
1.0.0 · Source§fn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read moreSource§impl Debug for FakeReadCause
impl Debug for FakeReadCause
Source§impl<__D: TyDecoder> Decodable<__D> for FakeReadCause
impl<__D: TyDecoder> Decodable<__D> for FakeReadCause
Source§impl<__E: TyEncoder> Encodable<__E> for FakeReadCause
impl<__E: TyEncoder> Encodable<__E> for FakeReadCause
Source§impl Hash for FakeReadCause
impl Hash for FakeReadCause
Source§impl<'__ctx> HashStable<StableHashingContext<'__ctx>> for FakeReadCause
impl<'__ctx> HashStable<StableHashingContext<'__ctx>> for FakeReadCause
fn hash_stable( &self, __hcx: &mut StableHashingContext<'__ctx>, __hasher: &mut StableHasher, )
Source§impl PartialEq for FakeReadCause
impl PartialEq for FakeReadCause
Source§impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for FakeReadCause
impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for FakeReadCause
Source§fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
self,
_: &mut F,
) -> Result<Self, F::Error>
fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>( self, _: &mut F, ) -> Result<Self, F::Error>
Source§impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for FakeReadCause
impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for FakeReadCause
Source§fn visit_with<F: TypeVisitor<TyCtxt<'tcx>>>(&self, _: &mut F) -> F::Result
fn visit_with<F: TypeVisitor<TyCtxt<'tcx>>>(&self, _: &mut F) -> F::Result
impl Copy for FakeReadCause
impl StructuralPartialEq for FakeReadCause
Auto Trait Implementations§
impl DynSend for FakeReadCause
impl DynSync for FakeReadCause
impl Freeze for FakeReadCause
impl RefUnwindSafe for FakeReadCause
impl Send for FakeReadCause
impl Sync for FakeReadCause
impl Unpin for FakeReadCause
impl UnwindSafe for FakeReadCause
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Size: 8 bytes
Size for each variant:
ForMatchGuard
: 0 bytesForMatchedPlace
: 4 bytesForGuardBinding
: 0 bytesForLet
: 4 bytesForIndex
: 0 bytes