Struct regex_automata::nfa::thompson::pikevm::Config

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pub struct Config { /* private fields */ }

Available on crate features nfa-thompson and nfa-pikevm only.

Expand description

The configuration used for building a PikeVM.

A PikeVM configuration is a simple data object that is typically used with Builder::configure. It can be cheaply cloned.

A default configuration can be created either with Config::new, or perhaps more conveniently, with PikeVM::config.

Implementations§

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impl Config

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pub fn new() -> Config

Return a new default PikeVM configuration.

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pub fn match_kind(self, kind: MatchKind) -> Config

Set the desired match semantics.

The default is MatchKind::LeftmostFirst, which corresponds to the match semantics of Perl-like regex engines. That is, when multiple patterns would match at the same leftmost position, the pattern that appears first in the concrete syntax is chosen.

Currently, the only other kind of match semantics supported is MatchKind::All. This corresponds to “classical DFA” construction where all possible matches are visited in the NFA by the PikeVM.

Typically, All is used when one wants to execute an overlapping search and LeftmostFirst otherwise. In particular, it rarely makes sense to use All with the various “leftmost” find routines, since the leftmost routines depend on the LeftmostFirst automata construction strategy. Specifically, LeftmostFirst results in the PikeVM simulating dead states as a way to terminate the search and report a match. LeftmostFirst also supports non-greedy matches using this strategy where as All does not.

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pub fn prefilter(self, pre: Option<Prefilter>) -> Config

Set a prefilter to be used whenever a start state is entered.

A Prefilter in this context is meant to accelerate searches by looking for literal prefixes that every match for the corresponding pattern (or patterns) must start with. Once a prefilter produces a match, the underlying search routine continues on to try and confirm the match.

Be warned that setting a prefilter does not guarantee that the search will be faster. While it’s usually a good bet, if the prefilter produces a lot of false positive candidates (i.e., positions matched by the prefilter but not by the regex), then the overall result can be slower than if you had just executed the regex engine without any prefilters.

By default no prefilter is set.

§Example

use regex_automata::{
    nfa::thompson::pikevm::PikeVM,
    util::prefilter::Prefilter,
    Input, Match, MatchKind,
};

let pre = Prefilter::new(MatchKind::LeftmostFirst, &["foo", "bar"]);
let re = PikeVM::builder()
    .configure(PikeVM::config().prefilter(pre))
    .build(r"(foo|bar)[a-z]+")?;
let mut cache = re.create_cache();
let input = Input::new("foo1 barfox bar");
assert_eq!(Some(Match::must(0, 5..11)), re.find(&mut cache, input));

Be warned though that an incorrect prefilter can lead to incorrect results!

use regex_automata::{
    nfa::thompson::pikevm::PikeVM,
    util::prefilter::Prefilter,
    Input, HalfMatch, MatchKind,
};

let pre = Prefilter::new(MatchKind::LeftmostFirst, &["foo", "car"]);
let re = PikeVM::builder()
    .configure(PikeVM::config().prefilter(pre))
    .build(r"(foo|bar)[a-z]+")?;
let mut cache = re.create_cache();
let input = Input::new("foo1 barfox bar");
// No match reported even though there clearly is one!
assert_eq!(None, re.find(&mut cache, input));