Function is_match

pub fn is_match<C: Cursor>(
    vm: &PikeVM,
    cache: &mut Cache,
    input: &mut Input<C>,
) -> bool

Returns true if and only if this PikeVM matches the given haystack.

This routine may short circuit if it knows that scanning future input will never lead to a different result. In particular, if the underlying NFA enters a match state, then this routine will return true immediately without inspecting any future input. (Consider how this might make a difference given the regex a+ on the haystack aaaaaaaaaaaaaaa. This routine can stop after it sees the first a, but routines like find need to continue searching because + is greedy by default.)

Example

This shows basic usage:

use regex_automata::nfa::thompson::pikevm::PikeVM;

let re = PikeVM::new("foo[0-9]+bar")?;
let mut cache = re.create_cache();

assert!(re.is_match(&mut cache, "foo12345bar"));
assert!(!re.is_match(&mut cache, "foobar"));

Example: consistency with search APIs

is_match is guaranteed to return true whenever find returns a match. This includes searches that are executed entirely within a codepoint:

use regex_automata::{nfa::thompson::pikevm::PikeVM, Input};

let re = PikeVM::new("a*")?;
let mut cache = re.create_cache();

assert!(!re.is_match(&mut cache, Input::new("☃").span(1..2)));

Notice that when UTF-8 mode is disabled, then the above reports a match because the restriction against zero-width matches that split a codepoint has been lifted:

use regex_automata::{nfa::thompson::{pikevm::PikeVM, NFA}, Input};

let re = PikeVM::builder()
    .thompson(NFA::config().utf8(false))
    .build("a*")?;
let mut cache = re.create_cache();

assert!(re.is_match(&mut cache, Input::new("☃").span(1..2)));