Type Alias rustc_mir_dataflow::move_paths::abs_domain::AbstractElem

pub type AbstractElem = ProjectionElem<AbstractOperand, AbstractType>;

Aliased Type

enum AbstractElem {
    Deref,
    Field(FieldIdx, AbstractType),
    Index(AbstractOperand),
    ConstantIndex {
        offset: u64,
        min_length: u64,
        from_end: bool,
    },
    Subslice {
        from: u64,
        to: u64,
        from_end: bool,
    },
    Downcast(Option<Symbol>, VariantIdx),
    OpaqueCast(AbstractType),
}

Variants

Deref

Field(FieldIdx, AbstractType)

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(AbstractOperand)

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(AbstractType)

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

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:24 bytes

Size for each variant:

• Deref: 0 bytes
• Field: 7 bytes
• Index: 0 bytes
• ConstantIndex: 23 bytes
• Subslice: 23 bytes
• Downcast: 11 bytes
• OpaqueCast: 0 bytes