Struct Match

pub struct Match<'h> { /* private fields */ }

Represents a single match of a regex in a haystack.

A Match contains both the start and end byte offsets of the match and the actual substring corresponding to the range of those byte offsets. It is guaranteed that start <= end. When start == end, the match is empty.

Unlike the top-level Match type, this Match type is produced by APIs that search &[u8] haystacks. This means that the offsets in a Match can point to anywhere in the haystack, including in a place that splits the UTF-8 encoding of a Unicode scalar value.

The lifetime parameter 'h refers to the lifetime of the matched of the haystack that this match was produced from.

Numbering

The byte offsets in a Match form a half-open interval. That is, the start of the range is inclusive and the end of the range is exclusive. For example, given a haystack abcFOOxyz and a match of FOO, its byte offset range starts at 3 and ends at 6. 3 corresponds to F and 6 corresponds to x, which is one past the end of the match. This corresponds to the same kind of slicing that Rust uses.

For more on why this was chosen over other schemes (aside from being consistent with how Rust the language works), see this discussion and Dijkstra’s note on a related topic.

Example

This example shows the value of each of the methods on Match for a particular search.

use regex::bytes::Regex;

let re = Regex::new(r"\p{Greek}+").unwrap();
let hay = "Greek: αβγδ".as_bytes();
let m = re.find(hay).unwrap();
assert_eq!(7, m.start());
assert_eq!(15, m.end());
assert!(!m.is_empty());
assert_eq!(8, m.len());
assert_eq!(7..15, m.range());
assert_eq!("αβγδ".as_bytes(), m.as_bytes());

Implementations

impl<'h> Match<'h>

pub fn start(&self) -> usize

Returns the byte offset of the start of the match in the haystack. The start of the match corresponds to the position where the match begins and includes the first byte in the match.

It is guaranteed that Match::start() <= Match::end().

Unlike the top-level Match type, the start offset may appear anywhere in the haystack. This includes between the code units of a UTF-8 encoded Unicode scalar value.

pub fn end(&self) -> usize

Returns the byte offset of the end of the match in the haystack. The end of the match corresponds to the byte immediately following the last byte in the match. This means that &slice[start..end] works as one would expect.

It is guaranteed that Match::start() <= Match::end().

Unlike the top-level Match type, the start offset may appear anywhere in the haystack. This includes between the code units of a UTF-8 encoded Unicode scalar value.

pub fn is_empty(&self) -> bool

Returns true if and only if this match has a length of zero.

Note that an empty match can only occur when the regex itself can match the empty string. Here are some examples of regexes that can all match the empty string: ^, ^$, \b, a?, a*, a{0}, (foo|\d+|quux)?.

pub fn len(&self) -> usize

Returns the length, in bytes, of this match.

pub fn range(&self) -> Range<usize>

Returns the range over the starting and ending byte offsets of the match in the haystack.

pub fn as_bytes(&self) -> &'h [u8]

Returns the substring of the haystack that matched.

Trait Implementations

impl<'h> Clone for Match<'h>

fn clone(&self) -> Match<'h>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<'h> Debug for Match<'h>

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

Formats the value using the given formatter.

impl<'h> From<Match<'h>> for &'h [u8]

fn from(m: Match<'h>) -> &'h [u8]

Converts to this type from the input type.

impl<'h> PartialEq for Match<'h>

fn eq(&self, other: &Match<'h>) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<'h> Copy for Match<'h>

impl<'h> Eq for Match<'h>

impl<'h> StructuralPartialEq for Match<'h>