Enum rustc_mir_build::thir::pattern::usefulness::Usefulness

enum Usefulness<'p, 'tcx> {
    NoWitnesses {
        useful: bool,
    },
    WithWitnesses(Vec<Witness<'p, 'tcx>>),
}

This carries the results of computing usefulness, as described at the top of the file. When checking usefulness of a match branch, we use the NoWitnesses variant, which also keeps track of potential unreachable sub-patterns (in the presence of or-patterns). When checking exhaustiveness of a whole match, we use the WithWitnesses variant, which carries a list of witnesses of non-exhaustiveness when there are any. Which variant to use is dictated by ArmType.

Variants

NoWitnesses

Fields

useful: bool

If we don’t care about witnesses, simply remember if the pattern was useful.

WithWitnesses(Vec<Witness<'p, 'tcx>>)

Carries a list of witnesses of non-exhaustiveness. If empty, indicates that the whole pattern is unreachable.

Implementations

impl<'p, 'tcx> Usefulness<'p, 'tcx>

fn new_useful(preference: ArmType) -> Self

fn new_not_useful(preference: ArmType) -> Self

fn is_useful(&self) -> bool

fn extend(&mut self, other: Self)

Combine usefulnesses from two branches. This is an associative operation.

fn apply_constructor(
    self,
    pcx: &PatCtxt<'_, 'p, 'tcx>,
    matrix: &Matrix<'p, 'tcx>,
    ctor: &Constructor<'tcx>
) -> Self

After calculating usefulness after a specialization, call this to reconstruct a usefulness that makes sense for the matrix pre-specialization. This new usefulness can then be merged with the results of specializing with the other constructors.

Trait Implementations

impl<'p, 'tcx> Debug for Usefulness<'p, 'tcx>

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: 24 bytes

Size for each variant:

• NoWitnesses: 1 byte
• WithWitnesses: 24 bytes