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.

Since this Match can only be produced by the top-level Regex APIs that only support searching UTF-8 encoded strings, the byte offsets for a Match are guaranteed to fall on valid UTF-8 codepoint boundaries. That is, slicing a &str with Match::range is guaranteed to never panic.

Values with this type are created by Regex::find or Regex::find_iter. Other APIs can create Match values too. For example, Captures::get.

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::Regex;

let re = Regex::new(r"\p{Greek}+").unwrap();
let hay = "Greek: αβγδ";
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", m.as_str());

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().

This is guaranteed to fall on a valid UTF-8 codepoint boundary. That is, it will never be an offset that appears between the UTF-8 code units of a UTF-8 encoded Unicode scalar value. Consequently, it is always safe to slice the corresponding haystack using this offset.

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().

This is guaranteed to fall on a valid UTF-8 codepoint boundary. That is, it will never be an offset that appears between the UTF-8 code units of a UTF-8 encoded Unicode scalar value. Consequently, it is always safe to slice the corresponding haystack using this offset.

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.

It is always correct to slice the original haystack searched with this range. That is, because the offsets are guaranteed to fall on valid UTF-8 boundaries, the range returned is always valid.

pub fn as_str(&self) -> &'h str

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 str

fn from(m: Match<'h>) -> &'h str

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>