Enum rustc_middle::mir::ProjectionElem

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pub enum ProjectionElem<V, T> {
    Deref,
    Field(FieldIdx, T),
    Index(V),
    ConstantIndex {
        offset: u64,
        min_length: u64,
        from_end: bool,
    },
    Subslice {
        from: u64,
        to: u64,
        from_end: bool,
    },
    Downcast(Option<Symbol>, VariantIdx),
    OpaqueCast(T),
    Subtype(T),
}

Variants§

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Deref

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Field(FieldIdx, T)

A field (e.g., f in _1.f) is one variant of ProjectionElem. Conceptually, rustc can identify that a field projection refers to either two different regions of memory or the same one between the base and the ‘projection element’. Read more about projections in the rustc-dev-guide

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Index(V)

Index into a slice/array.

Note that this does not also dereference, and so it does not exactly correspond to slice indexing in Rust. In other words, in the below Rust code:

let x = &[1, 2, 3, 4];
let i = 2;
x[i];

The x[i] is turned into a Deref followed by an Index, not just an Index. The same thing is true of the ConstantIndex and Subslice projections below.

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ConstantIndex

These indices are generated by slice patterns. Easiest to explain by example:

[X, _, .._, _, _] => { offset: 0, min_length: 4, from_end: false },
[_, X, .._, _, _] => { offset: 1, min_length: 4, from_end: false },
[_, _, .._, X, _] => { offset: 2, min_length: 4, from_end: true },
[_, _, .._, _, X] => { offset: 1, min_length: 4, from_end: true },

Fields

§offset: u64

index or -index (in Python terms), depending on from_end

§min_length: u64

The thing being indexed must be at least this long. For arrays this is always the exact length.

§from_end: bool

Counting backwards from end? This is always false when indexing an array.

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Subslice

These indices are generated by slice patterns.

If from_end is true slice[from..slice.len() - to]. Otherwise array[from..to].

Fields

§from: u64
§to: u64
§from_end: bool

Whether to counts from the start or end of the array/slice. For PlaceElems this is true if and only if the base is a slice. For ProjectionKind, this can also be true for arrays.

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Downcast(Option<Symbol>, VariantIdx)

“Downcast” to a variant of an enum or a coroutine.

The included Symbol is the name of the variant, used for printing MIR.

This operation itself is never UB, all it does is change the type of the place.

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OpaqueCast(T)

Like an explicit cast from an opaque type to a concrete type, but without requiring an intermediate variable.

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Subtype(T)

A Subtype(T) projection is applied to any StatementKind::Assign where type of lvalue doesn’t match the type of rvalue, the primary goal is making subtyping explicit during optimizations and codegen.

This projection doesn’t impact the runtime behavior of the program except for potentially changing some type metadata of the interpreter or codegen backend.

This goal is achieved with mir_transform pass Subtyper, which runs right after borrowchecker, as we only care about subtyping that can affect trait selection and TypeId.

Implementations§

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impl<V, T> ProjectionElem<V, T>

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fn is_indirect(&self) -> bool

Returns true if the target of this projection may refer to a different region of memory than the base.

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pub fn is_stable_offset(&self) -> bool

Returns true if the target of this projection always refers to the same memory region whatever the state of the program.

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pub fn is_downcast_to(&self, v: VariantIdx) -> bool

Returns true if this is a Downcast projection with the given VariantIdx.

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pub fn is_field_to(&self, f: FieldIdx) -> bool

Returns true if this is a Field projection with the given index.

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pub fn can_use_in_debuginfo(&self) -> bool

Returns true if this is accepted inside VarDebugInfoContents::Place.

Trait Implementations§

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impl<V: Clone, T: Clone> Clone for ProjectionElem<V, T>

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fn clone(&self) -> ProjectionElem<V, T>

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl<V: Debug, T: Debug> Debug for ProjectionElem<V, T>

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

Formats the value using the given formatter. Read more
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impl<V, T, __D: TyDecoder> Decodable<__D> for ProjectionElem<V, T>
where T: Decodable<__D>, V: Decodable<__D>,

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

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impl<V, T, __E: TyEncoder> Encodable<__E> for ProjectionElem<V, T>
where T: Encodable<__E>, V: Encodable<__E>,

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

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impl<V: Hash, T: Hash> Hash for ProjectionElem<V, T>

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fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher. Read more
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fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher. Read more
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impl<'__ctx, V, T> HashStable<StableHashingContext<'__ctx>> for ProjectionElem<V, T>

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

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impl<V: Ord, T: Ord> Ord for ProjectionElem<V, T>

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fn cmp(&self, other: &ProjectionElem<V, T>) -> Ordering

This method returns an Ordering between self and other. Read more
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fn max(self, other: Self) -> Self
where Self: Sized,

Compares and returns the maximum of two values. Read more
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fn min(self, other: Self) -> Self
where Self: Sized,

Compares and returns the minimum of two values. Read more
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fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized + PartialOrd,

Restrict a value to a certain interval. Read more
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impl<V: PartialEq, T: PartialEq> PartialEq for ProjectionElem<V, T>

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fn eq(&self, other: &ProjectionElem<V, T>) -> bool

This method tests for self and other values to be equal, and is used by ==.
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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.
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impl<V: PartialOrd, T: PartialOrd> PartialOrd for ProjectionElem<V, T>

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fn partial_cmp(&self, other: &ProjectionElem<V, T>) -> Option<Ordering>

This method returns an ordering between self and other values if one exists. Read more
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fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator. Read more
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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
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fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator. Read more
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fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more
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impl<'tcx, V, T> TypeFoldable<TyCtxt<'tcx>> for ProjectionElem<V, T>
where T: TypeFoldable<TyCtxt<'tcx>>, V: TypeFoldable<TyCtxt<'tcx>>,

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fn try_fold_with<__F: FallibleTypeFolder<TyCtxt<'tcx>>>( self, __folder: &mut __F, ) -> Result<Self, __F::Error>

The entry point for folding. To fold a value t with a folder f call: t.try_fold_with(f). Read more
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fn fold_with<F>(self, folder: &mut F) -> Self
where F: TypeFolder<I>,

A convenient alternative to try_fold_with for use with infallible folders. Do not override this method, to ensure coherence with try_fold_with.
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impl<'tcx, V, T> TypeVisitable<TyCtxt<'tcx>> for ProjectionElem<V, T>
where T: TypeVisitable<TyCtxt<'tcx>>, V: TypeVisitable<TyCtxt<'tcx>>,

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fn visit_with<__V: TypeVisitor<TyCtxt<'tcx>>>( &self, __visitor: &mut __V, ) -> __V::Result

The entry point for visiting. To visit a value t with a visitor v call: t.visit_with(v). Read more
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impl<V: Copy, T: Copy> Copy for ProjectionElem<V, T>

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impl<V: Eq, T: Eq> Eq for ProjectionElem<V, T>

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impl<V, T> StructuralPartialEq for ProjectionElem<V, T>

Auto Trait Implementations§

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impl<V, T> Freeze for ProjectionElem<V, T>
where T: Freeze, V: Freeze,

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impl<V, T> RefUnwindSafe for ProjectionElem<V, T>

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impl<V, T> Send for ProjectionElem<V, T>
where T: Send, V: Send,

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impl<V, T> Sync for ProjectionElem<V, T>
where T: Sync, V: Sync,

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impl<V, T> Unpin for ProjectionElem<V, T>
where T: Unpin, V: Unpin,

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impl<V, T> UnwindSafe for ProjectionElem<V, T>
where T: UnwindSafe, V: UnwindSafe,

Blanket Implementations§

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impl<T> Aligned for T

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const ALIGN: Alignment = _

Alignment of Self.
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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> AnyEq for T
where T: Any + PartialEq,

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fn equals(&self, other: &(dyn Any + 'static)) -> bool

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fn as_any(&self) -> &(dyn Any + 'static)

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impl<'tcx, T> ArenaAllocatable<'tcx, IsCopy> for T
where T: Copy,

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fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut T

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fn allocate_from_iter<'a>( arena: &'a Arena<'tcx>, iter: impl IntoIterator<Item = T>, ) -> &'a mut [T]

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impl<'tcx, T> ArenaAllocatable<'tcx, IsCopy> for T
where T: Copy,

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fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut T

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fn allocate_from_iter<'a>( arena: &'a Arena<'tcx>, iter: impl IntoIterator<Item = T>, ) -> &'a mut [T]

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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> CloneToUninit for T
where T: Copy,

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unsafe fn clone_to_uninit(&self, dst: *mut T)

🔬This is a nightly-only experimental API. (clone_to_uninit)
Performs copy-assignment from self to dst. Read more
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impl<T> CloneToUninit for T
where T: Clone,

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default unsafe fn clone_to_uninit(&self, dst: *mut T)

🔬This is a nightly-only experimental API. (clone_to_uninit)
Performs copy-assignment from self to dst. Read more
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impl<T, R> CollectAndApply<T, R> for T

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fn collect_and_apply<I, F>(iter: I, f: F) -> R
where I: Iterator<Item = T>, F: FnOnce(&[T]) -> R,

Equivalent to f(&iter.collect::<Vec<_>>()).

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type Output = R

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impl<Q, K> Comparable<K> for Q
where Q: Ord + ?Sized, K: Borrow<Q> + ?Sized,

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fn compare(&self, key: &K) -> Ordering

Compare self to key and return their ordering.
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impl<Tcx, T> DepNodeParams<Tcx> for T
where Tcx: DepContext, T: for<'a> HashStable<StableHashingContext<'a>> + Debug,

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default fn fingerprint_style() -> FingerprintStyle

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default fn to_fingerprint(&self, tcx: Tcx) -> 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).
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default fn to_debug_str(&self, _: Tcx) -> String

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default fn recover(_: Tcx, _: &DepNode) -> Option<T>

This method tries to recover the query key from the given DepNode, something which is needed when forcing DepNodes 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.
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impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Checks if this value is equivalent to the given key. Read more
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impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Checks if this value is equivalent to the given key. Read more
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impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Compare self to key and return true if they are equal.
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impl<T> Filterable for T

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fn filterable( self, filter_name: &'static str, ) -> RequestFilterDataProvider<T, fn(_: DataRequest<'_>) -> bool>

Creates a filterable data provider with the given name for debugging. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T> Instrument for T

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fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
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fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current Span, returning an Instrumented wrapper. Read more
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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> IntoEither for T

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fn into_either(self, into_left: bool) -> Either<Self, Self>

Converts self into a Left variant of Either<Self, Self> if into_left is true. Converts self into a Right variant of Either<Self, Self> otherwise. Read more
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fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
where F: FnOnce(&Self) -> bool,

Converts self into a Left variant of Either<Self, Self> if into_left(&self) returns true. Converts self into a Right variant of Either<Self, Self> otherwise. Read more
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impl<P> IntoQueryParam<P> for P

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impl<'tcx, T> IsSuggestable<'tcx> for T
where T: TypeVisitable<TyCtxt<'tcx>> + TypeFoldable<TyCtxt<'tcx>>,

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fn is_suggestable(self, tcx: TyCtxt<'tcx>, infer_suggestable: bool) -> bool

Whether this makes sense to suggest in a diagnostic. Read more
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fn make_suggestable( self, tcx: TyCtxt<'tcx>, infer_suggestable: bool, placeholder: Option<Ty<'tcx>>, ) -> Option<T>

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impl<T> MaybeResult<T> for T

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type Error = !

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fn from(_: Result<T, <T as MaybeResult<T>>::Error>) -> T

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fn to_result(self) -> Result<T, <T as MaybeResult<T>>::Error>

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impl<T> Same for T

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type Output = T

Should always be Self
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impl<T> ToOwned for T
where T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<I, T> TypeVisitableExt<I> for T
where I: Interner, T: TypeVisitable<I>,

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

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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.
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fn error_reported(&self) -> Result<(), <I as Interner>::ErrorGuaranteed>

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

Returns true if this type has any regions that escape binder (and hence are not bound by it).
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fn has_escaping_bound_vars(&self) -> bool

Return true if this type has regions that are not a part of the type. For example, for<'a> fn(&'a i32) return false, while fn(&'a i32) would return true. The latter can occur when traversing through the former. Read more
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fn has_aliases(&self) -> bool

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fn has_inherent_projections(&self) -> bool

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fn has_opaque_types(&self) -> bool

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fn has_coroutines(&self) -> bool

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fn references_error(&self) -> bool

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fn has_non_region_param(&self) -> bool

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fn has_infer_regions(&self) -> bool

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fn has_infer_types(&self) -> bool

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fn has_non_region_infer(&self) -> bool

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fn has_infer(&self) -> bool

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fn has_placeholders(&self) -> bool

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fn has_non_region_placeholders(&self) -> bool

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fn has_param(&self) -> bool

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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.
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fn has_erased_regions(&self) -> bool

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fn has_erasable_regions(&self) -> bool

True if there are any un-erased free regions.
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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.
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fn has_bound_regions(&self) -> bool

True if there are any late-bound regions
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fn has_non_region_bound_vars(&self) -> bool

True if there are any late-bound non-region variables
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fn has_bound_vars(&self) -> bool

True if there are any bound variables
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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.
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impl<I, T, U> Upcast<I, U> for T
where U: UpcastFrom<I, T>,

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fn upcast(self, interner: I) -> U

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impl<I, T> UpcastFrom<I, T> for T

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fn upcast_from(from: T, _tcx: I) -> T

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impl<V, T> VZip<V> for T
where V: MultiLane<T>,

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fn vzip(self) -> V

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impl<Tcx, T> Value<Tcx> for T
where Tcx: DepContext,

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default fn from_cycle_error( tcx: Tcx, cycle_error: &CycleError, _guar: ErrorGuaranteed, ) -> T

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impl<T> WithSubscriber for T

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fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
where S: Into<Dispatch>,

Attaches the provided Subscriber to this type, returning a WithDispatch wrapper. Read more
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fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default Subscriber to this type, returning a WithDispatch wrapper. Read more
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impl<'a, T> Captures<'a> for T
where T: ?Sized,

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impl<T> ErasedDestructor for T
where T: 'static,

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impl<T> MaybeSendSync for T

Layout§

Note: Unable to compute type layout, possibly due to this type having generic parameters. Layout can only be computed for concrete, fully-instantiated types.