Struct rustc_pattern_analysis::usefulness::MatrixRow

struct MatrixRow<'p, Cx: PatCx> {
    pats: PatStack<'p, Cx>,
    is_under_guard: bool,
    parent_row: usize,
    useful: bool,
    intersects_at_least: BitSet<usize>,
    head_is_branch: bool,
}

A row of the matrix.

Fields

pats: PatStack<'p, Cx>

is_under_guard: bool

Whether the original arm had a guard. This is inherited when specializing.

parent_row: usize

When we specialize, we remember which row of the original matrix produced a given row of the specialized matrix. When we unspecialize, we use this to propagate usefulness back up the callstack. On creation, this stores the index of the original match arm.

useful: bool

False when the matrix is just built. This is set to true by compute_exhaustiveness_and_usefulness if the arm is found to be useful. This is reset to false when specializing.

intersects_at_least: BitSet<usize>

Tracks some rows above this one that have an intersection with this one, i.e. such that there is a value that matches both rows. Because of relevancy we may miss some intersections. The intersections we do find are correct. In other words, this is an underapproximation of the real set of intersections.

For example:

match ... {
    (true, _, _) => {} // `intersects_at_least = []`
    (_, true, 0..=10) => {} // `intersects_at_least = []`
    (_, true, 5..15) => {} // `intersects_at_least = [1]`
}

Here the (true, true) case is irrelevant. Since we skip it, we will not detect that row 0 intersects rows 1 and 2.

head_is_branch: bool

Whether the head pattern is a branch (see definition of “branch pattern” at BranchPatUsefulness)

Implementations

impl<'p, Cx: PatCx> MatrixRow<'p, Cx>

fn new(arm: &MatchArm<'p, Cx>, arm_id: usize) -> Self

fn len(&self) -> usize

fn head(&self) -> PatOrWild<'p, Cx>

fn iter(&self) -> impl Iterator<Item = PatOrWild<'p, Cx>> + Captures<'_>

fn expand_or_pat( &self, parent_row: usize, ) -> impl Iterator<Item = MatrixRow<'p, Cx>> + Captures<'_>

fn pop_head_constructor( &self, cx: &Cx, ctor: &Constructor<Cx>, ctor_arity: usize, ctor_is_relevant: bool, parent_row: usize, ) -> Result<MatrixRow<'p, Cx>, Cx::Error>

This computes specialize(ctor, self). See top of the file for explanations. Only call if ctor.is_covered_by(self.head().ctor()) is true.

Trait Implementations

impl<'p, Cx: Clone + PatCx> Clone for MatrixRow<'p, Cx>

fn clone(&self) -> MatrixRow<'p, Cx>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<'p, Cx: PatCx> Debug for MatrixRow<'p, Cx>

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

Formats the value using the given formatter.

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: 80 bytes