Enum regex_automata::util::start::Start

pub(crate) enum Start {
    NonWordByte = 0,
    WordByte = 1,
    Text = 2,
    LineLF = 3,
    LineCR = 4,
    CustomLineTerminator = 5,
}

Represents the six possible starting configurations of a DFA search.

The starting configuration is determined by inspecting the beginning of the haystack (up to 1 byte). Ultimately, this along with a pattern ID (if specified) and the type of search (anchored or not) is what selects the start state to use in a DFA.

As one example, if a DFA only supports unanchored searches and does not support anchored searches for each pattern, then it will have at most 6 distinct start states. (Some start states may be reused if determinization can determine that they will be equivalent.) If the DFA supports both anchored and unanchored searches, then it will have a maximum of 12 distinct start states. Finally, if the DFA also supports anchored searches for each pattern, then it can have up to 12 + (N * 6) start states, where N is the number of patterns.

Handling each of these starting configurations in the context of DFA determinization can be quite tricky and subtle. But the code is small and can be found at crate::util::determinize::set_lookbehind_from_start.

Variants

NonWordByte = 0

This occurs when the starting position is not any of the ones below.

WordByte = 1

This occurs when the byte immediately preceding the start of the search is an ASCII word byte.

Text = 2

This occurs when the starting position of the search corresponds to the beginning of the haystack.

LineLF = 3

This occurs when the byte immediately preceding the start of the search is a line terminator. Specifically, \n.

LineCR = 4

This occurs when the byte immediately preceding the start of the search is a line terminator. Specifically, \r.

CustomLineTerminator = 5

This occurs when a custom line terminator has been set via a LookMatcher, and when that line terminator is neither a \r or a \n.

If the custom line terminator is a word byte, then this start configuration is still selected. DFAs that implement word boundary assertions will likely need to check whether the custom line terminator is a word byte, in which case, it should behave as if the byte satisfies \b in addition to multi-line anchors.

Implementations

impl Start

pub(crate) fn from_usize(n: usize) -> Option<Start>

Return the starting state corresponding to the given integer. If no starting state exists for the given integer, then None is returned.

pub(crate) fn len() -> usize

Returns the total number of starting state configurations.

pub(crate) fn as_u8(&self) -> u8

Return this starting configuration as u8 integer. It is guaranteed to be less than Start::len().

pub(crate) fn as_usize(&self) -> usize

Return this starting configuration as a usize integer. It is guaranteed to be less than Start::len().

Trait Implementations

impl Clone for Start

fn clone(&self) -> Start

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for Start

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

Formats the value using the given formatter.

impl PartialEq for Start

fn eq(&self, other: &Start) -> 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 Copy for Start

impl Eq for Start

impl StructuralPartialEq for Start