Enum rustc_middle::mir::syntax::ProjectionElem

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),
}

Variants

Deref

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

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.

ConstantIndex

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.

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 },

Subslice

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.

These indices are generated by slice patterns.

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

Downcast(Option<Symbol>, VariantIdx)

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

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

OpaqueCast(T)

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

Implementations

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

fn is_indirect(&self) -> bool

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

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.

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

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

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

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

pub fn can_use_in_debuginfo(&self) -> bool

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

Trait Implementations

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

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

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

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

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

Formats the value using the given formatter.

impl<'tcx, V, T, __D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<__D> for ProjectionElem<V, T>where T: Decodable<__D>, V: Decodable<__D>,

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

impl<'tcx, V, T, __E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<__E> for ProjectionElem<V, T>where T: Encodable<__E>, V: Encodable<__E>,

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

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

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, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<'__ctx, V, T> HashStable<StableHashingContext<'__ctx>> for ProjectionElem<V, T>where T: HashStable<StableHashingContext<'__ctx>>, V: HashStable<StableHashingContext<'__ctx>>,

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

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

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

This method returns an Ordering between self and other.

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

Compares and returns the maximum of two values.

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

Compares and returns the minimum of two values.

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

Restrict a value to a certain interval.

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

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

fn partial_cmp(&self, other: &ProjectionElem<V, T>) -> 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, V, T> TypeFoldable<TyCtxt<'tcx>> for ProjectionElem<V, T>where T: TypeFoldable<TyCtxt<'tcx>>, V: TypeFoldable<TyCtxt<'tcx>>,

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).

fn fold_with<F>(self, folder: &mut F) -> Selfwhere 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.

impl<'tcx, V, T> TypeVisitable<TyCtxt<'tcx>> for ProjectionElem<V, T>where T: TypeVisitable<TyCtxt<'tcx>>, V: TypeVisitable<TyCtxt<'tcx>>,

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

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

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

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

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

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