Trait regex_automata::DFA

source · 
pub trait DFA {
    type ID: StateID;


Show 15 methods    fn start_state(&self) -> Self::ID;
    fn is_match_state(&self, id: Self::ID) -> bool;
    fn is_dead_state(&self, id: Self::ID) -> bool;
    fn is_match_or_dead_state(&self, id: Self::ID) -> bool;
    fn is_anchored(&self) -> bool;
    fn next_state(&self, current: Self::ID, input: u8) -> Self::ID;
    unsafe fn next_state_unchecked(
        &self,
        current: Self::ID,
        input: u8
    ) -> Self::ID;

    fn is_match(&self, bytes: &[u8]) -> bool { ... }
    fn shortest_match(&self, bytes: &[u8]) -> Option<usize> { ... }
    fn find(&self, bytes: &[u8]) -> Option<usize> { ... }
    fn rfind(&self, bytes: &[u8]) -> Option<usize> { ... }
    fn is_match_at(&self, bytes: &[u8], start: usize) -> bool { ... }
    fn shortest_match_at(&self, bytes: &[u8], start: usize) -> Option<usize> { ... }
    fn find_at(&self, bytes: &[u8], start: usize) -> Option<usize> { ... }
    fn rfind_at(&self, bytes: &[u8], start: usize) -> Option<usize> { ... }

}
Expand description

A trait describing the interface of a deterministic finite automaton (DFA).

Every DFA has exactly one start state and at least one dead state (which may be the same, as in the case of an empty DFA). In all cases, a state identifier of 0 must be a dead state such that DFA::is_dead_state(0) always returns true.

Every DFA also has zero or more match states, such that DFA::is_match_state(id) returns true if and only if id corresponds to a match state.

In general, users of this trait likely will only need to use the search routines such as is_match, shortest_match, find or rfind. The other methods are lower level and are used for walking the transitions of a DFA manually. In particular, the aforementioned search routines are implemented generically in terms of the lower level transition walking routines.

Required Associated Types§

The representation used for state identifiers in this DFA.

Typically, this is one of u8, u16, u32, u64 or usize.

Required Methods§

Return the identifier of this DFA’s start state.

Returns true if and only if the given identifier corresponds to a match state.

Returns true if and only if the given identifier corresponds to a dead state. When a DFA enters a dead state, it is impossible to leave and thus can never lead to a match.

Returns true if and only if the given identifier corresponds to either a dead state or a match state, such that one of is_match_state(id) or is_dead_state(id) must return true.

Depending on the implementation of the DFA, this routine can be used to save a branch in the core matching loop. Nevertheless, is_match_state(id) || is_dead_state(id) is always a valid implementation.

Returns true if and only if this DFA is anchored.

When a DFA is anchored, it is only allowed to report matches that start at index 0.

Given the current state that this DFA is in and the next input byte, this method returns the identifier of the next state. The identifier returned is always valid, but it may correspond to a dead state.

Like next_state, but its implementation may look up the next state without memory safety checks such as bounds checks. As such, callers must ensure that the given identifier corresponds to a valid DFA state. Implementors must, in turn, ensure that this routine is safe for all valid state identifiers and for all possible u8 values.

Provided Methods§

Returns true if and only if the given bytes match this DFA.

This routine may short circuit if it knows that scanning future input will never lead to a different result. In particular, if a DFA enters a match state or a dead state, then this routine will return true or false, respectively, without inspecting any future input.

Example

This example shows how to use this method with a DenseDFA.

use regex_automata::{DFA, DenseDFA};

let dfa = DenseDFA::new("foo[0-9]+bar")?;
assert_eq!(true, dfa.is_match(b"foo12345bar"));
assert_eq!(false, dfa.is_match(b"foobar"));

Returns the first position at which a match is found.

This routine stops scanning input in precisely the same circumstances as is_match. The key difference is that this routine returns the position at which it stopped scanning input if and only if a match was found. If no match is found, then None is returned.

Example

This example shows how to use this method with a DenseDFA.

use regex_automata::{DFA, DenseDFA};

let dfa = DenseDFA::new("foo[0-9]+")?;
assert_eq!(Some(4), dfa.shortest_match(b"foo12345"));

// Normally, the end of the leftmost first match here would be 3,
// but the shortest match semantics detect a match earlier.
let dfa = DenseDFA::new("abc|a")?;
assert_eq!(Some(1), dfa.shortest_match(b"abc"));

Returns the end offset of the longest match. If no match exists, then None is returned.

Implementors of this trait are not required to implement any particular match semantics (such as leftmost-first), which are instead manifest in the DFA’s topology itself.

In particular, this method must continue searching even after it enters a match state. The search should only terminate once it has reached the end of the input or when it has entered a dead state. Upon termination, the position of the last byte seen while still in a match state is returned.

Example

This example shows how to use this method with a DenseDFA. By default, a dense DFA uses “leftmost first” match semantics.

Leftmost first match semantics corresponds to the match with the smallest starting offset, but where the end offset is determined by preferring earlier branches in the original regular expression. For example, Sam|Samwise will match Sam in Samwise, but Samwise|Sam will match Samwise in Samwise.

Generally speaking, the “leftmost first” match is how most backtracking regular expressions tend to work. This is in contrast to POSIX-style regular expressions that yield “leftmost longest” matches. Namely, both Sam|Samwise and Samwise|Sam match Samwise when using leftmost longest semantics.

use regex_automata::{DFA, DenseDFA};

let dfa = DenseDFA::new("foo[0-9]+")?;
assert_eq!(Some(8), dfa.find(b"foo12345"));

// Even though a match is found after reading the first byte (`a`),
// the leftmost first match semantics demand that we find the earliest
// match that prefers earlier parts of the pattern over latter parts.
let dfa = DenseDFA::new("abc|a")?;
assert_eq!(Some(3), dfa.find(b"abc"));

Returns the start offset of the longest match in reverse, by searching from the end of the input towards the start of the input. If no match exists, then None is returned. In other words, this has the same match semantics as find, but in reverse.

Example

This example shows how to use this method with a DenseDFA. In particular, this routine is principally useful when used in conjunction with the dense::Builder::reverse configuration knob. In general, it’s unlikely to be correct to use both find and rfind with the same DFA since any particular DFA will only support searching in one direction.

use regex_automata::{dense, DFA};

let dfa = dense::Builder::new().reverse(true).build("foo[0-9]+")?;
assert_eq!(Some(0), dfa.rfind(b"foo12345"));

Returns the same as is_match, but starts the search at the given offset.

The significance of the starting point is that it takes the surrounding context into consideration. For example, if the DFA is anchored, then a match can only occur when start == 0.

Returns the same as shortest_match, but starts the search at the given offset.

The significance of the starting point is that it takes the surrounding context into consideration. For example, if the DFA is anchored, then a match can only occur when start == 0.

Returns the same as find, but starts the search at the given offset.

The significance of the starting point is that it takes the surrounding context into consideration. For example, if the DFA is anchored, then a match can only occur when start == 0.

Returns the same as rfind, but starts the search at the given offset.

The significance of the starting point is that it takes the surrounding context into consideration. For example, if the DFA is anchored, then a match can only occur when start == bytes.len().

Implementations on Foreign Types§

Implementors§