regexp.go

		}
		i++
	}

	// Parse number.
	num = 0
	for i := 0; i < len(name); i++ {
		if name[i] < '0' || '9' < name[i] || num >= 1e8 {
			num = -1
			break
		}
		num = num*10 + int(name[i]) - '0'
	}
	// Disallow leading zeros.
	if name[0] == '0' && len(name) > 1 {
		num = -1
	}

	rest = str[i:]
	ok = true
	return
}

// FindSubmatchIndex returns a slice holding the index pairs identifying the
// leftmost match of the regular expression in b and the matches, if any, of
// its subexpressions, as defined by the 'Submatch' and 'Index' descriptions
// in the package comment.
// A return value of nil indicates no match.
func (re *Regexp) FindSubmatchIndex(b []byte) []int {
	return re.pad(re.doExecute(nil, b, "", 0, re.prog.NumCap, nil))
}

// FindStringSubmatch returns a slice of strings holding the text of the
// leftmost match of the regular expression in s and the matches, if any, of
// its subexpressions, as defined by the 'Submatch' description in the
// package comment.
// A return value of nil indicates no match.
func (re *Regexp) FindStringSubmatch(s string) []string {
	var dstCap [4]int
	a := re.doExecute(nil, nil, s, 0, re.prog.NumCap, dstCap[:0])
	if a == nil {
		return nil
	}
	ret := make([]string, 1+re.numSubexp)
	for i := range ret {
		if 2*i < len(a) && a[2*i] >= 0 {
			ret[i] = s[a[2*i]:a[2*i+1]]
		}
	}
	return ret
}

// FindStringSubmatchIndex returns a slice holding the index pairs
// identifying the leftmost match of the regular expression in s and the
// matches, if any, of its subexpressions, as defined by the 'Submatch' and
// 'Index' descriptions in the package comment.
// A return value of nil indicates no match.
func (re *Regexp) FindStringSubmatchIndex(s string) []int {
	return re.pad(re.doExecute(nil, nil, s, 0, re.prog.NumCap, nil))
}

// FindReaderSubmatchIndex returns a slice holding the index pairs
// identifying the leftmost match of the regular expression of text read by
// the [io.RuneReader], and the matches, if any, of its subexpressions, as defined
// by the 'Submatch' and 'Index' descriptions in the package comment. A
// return value of nil indicates no match.
func (re *Regexp) FindReaderSubmatchIndex(r io.RuneReader) []int {
	return re.pad(re.doExecute(r, nil, "", 0, re.prog.NumCap, nil))
}

const startSize = 10 // The size at which to start a slice in the 'All' routines.

// FindAll is the 'All' version of [Regexp.Find]; it returns a slice of all successive
// matches of the expression, as defined by the 'All' description in the
// package comment.
// A return value of nil indicates no match.
func (re *Regexp) FindAll(b []byte, n int) [][]byte {
	if n < 0 {
		n = len(b) + 1
	}
	var result [][]byte
	re.allMatches("", b, n, func(match []int) {
		if result == nil {
			result = make([][]byte, 0, startSize)
		}
		result = append(result, b[match[0]:match[1]:match[1]])
	})
	return result
}

// FindAllIndex is the 'All' version of [Regexp.FindIndex]; it returns a slice of all
// successive matches of the expression, as defined by the 'All' description
// in the package comment.
// A return value of nil indicates no match.
func (re *Regexp) FindAllIndex(b []byte, n int) [][]int {
	if n < 0 {
		n = len(b) + 1
	}
	var result [][]int
	re.allMatches("", b, n, func(match []int) {
		if result == nil {
			result = make([][]int, 0, startSize)
		}
		result = append(result, match[0:2])
	})
	return result
}

// FindAllString is the 'All' version of [Regexp.FindString]; it returns a slice of all
// successive matches of the expression, as defined by the 'All' description
// in the package comment.
// A return value of nil indicates no match.
func (re *Regexp) FindAllString(s string, n int) []string {
	if n < 0 {
		n = len(s) + 1
	}
	var result []string
	re.allMatches(s, nil, n, func(match []int) {
		if result == nil {
			result = make([]string, 0, startSize)
		}
		result = append(result, s[match[0]:match[1]])
	})
	return result
}

// FindAllStringIndex is the 'All' version of [Regexp.FindStringIndex]; it returns a
// slice of all successive matches of the expression, as defined by the 'All'
// description in the package comment.
// A return value of nil indicates no match.
func (re *Regexp) FindAllStringIndex(s string, n int) [][]int {
	if n < 0 {
		n = len(s) + 1
	}
	var result [][]int
	re.allMatches(s, nil, n, func(match []int) {
		if result == nil {
			result = make([][]int, 0, startSize)
		}
		result = append(result, match[0:2])
	})
	return result
}

// FindAllSubmatch is the 'All' version of [Regexp.FindSubmatch]; it returns a slice
// of all successive matches of the expression, as defined by the 'All'
// description in the package comment.
// A return value of nil indicates no match.
func (re *Regexp) FindAllSubmatch(b []byte, n int) [][][]byte {
	if n < 0 {
		n = len(b) + 1
	}
	var result [][][]byte
	re.allMatches("", b, n, func(match []int) {
		if result == nil {
			result = make([][][]byte, 0, startSize)
		}
		slice := make([][]byte, len(match)/2)
		for j := range slice {
			if match[2*j] >= 0 {
				slice[j] = b[match[2*j]:match[2*j+1]:match[2*j+1]]
			}
		}
		result = append(result, slice)
	})
	return result
}

// FindAllSubmatchIndex is the 'All' version of [Regexp.FindSubmatchIndex]; it returns
// a slice of all successive matches of the expression, as defined by the
// 'All' description in the package comment.
// A return value of nil indicates no match.
func (re *Regexp) FindAllSubmatchIndex(b []byte, n int) [][]int {
	if n < 0 {
		n = len(b) + 1
	}
	var result [][]int
	re.allMatches("", b, n, func(match []int) {
		if result == nil {
			result = make([][]int, 0, startSize)
		}
		result = append(result, match)
	})
	return result
}

// FindAllStringSubmatch is the 'All' version of [Regexp.FindStringSubmatch]; it
// returns a slice of all successive matches of the expression, as defined by
// the 'All' description in the package comment.
// A return value of nil indicates no match.
func (re *Regexp) FindAllStringSubmatch(s string, n int) [][]string {
	if n < 0 {
		n = len(s) + 1
	}
	var result [][]string
	re.allMatches(s, nil, n, func(match []int) {
		if result == nil {
			result = make([][]string, 0, startSize)
		}
		slice := make([]string, len(match)/2)
		for j := range slice {
			if match[2*j] >= 0 {
				slice[j] = s[match[2*j]:match[2*j+1]]
			}
		}
		result = append(result, slice)
	})
	return result
}

// FindAllStringSubmatchIndex is the 'All' version of
// [Regexp.FindStringSubmatchIndex]; it returns a slice of all successive matches of
// the expression, as defined by the 'All' description in the package
// comment.
// A return value of nil indicates no match.
func (re *Regexp) FindAllStringSubmatchIndex(s string, n int) [][]int {
	if n < 0 {
		n = len(s) + 1
	}
	var result [][]int
	re.allMatches(s, nil, n, func(match []int) {
		if result == nil {
			result = make([][]int, 0, startSize)
		}
		result = append(result, match)
	})
	return result
}

// Split slices s into substrings separated by the expression and returns a slice of
// the substrings between those expression matches.
//
// The slice returned by this method consists of all the substrings of s
// not contained in the slice returned by [Regexp.FindAllString]. When called on an expression
// that contains no metacharacters, it is equivalent to [strings.SplitN].
//
// Example:
//
//	s := regexp.MustCompile("a*").Split("abaabaccadaaae", 5)
//	// s: ["", "b", "b", "c", "cadaaae"]
//
// The count determines the number of substrings to return:
//   - n > 0: at most n substrings; the last substring will be the unsplit remainder;
//   - n == 0: the result is nil (zero substrings);
//   - n < 0: all substrings.
func (re *Regexp) Split(s string, n int) []string {

	if n == 0 {
		return nil
	}

	if len(re.expr) > 0 && len(s) == 0 {
		return []string{""}
	}

	matches := re.FindAllStringIndex(s, n)
	strings := make([]string, 0, len(matches))

	beg := 0
	end := 0
	for _, match := range matches {
		if n > 0 && len(strings) >= n-1 {
			break
		}

		end = match[0]
		if match[1] != 0 {
			strings = append(strings, s[beg:end])
		}
		beg = match[1]
	}

	if end != len(s) {
		strings = append(strings, s[beg:])
	}

	return strings
}

// AppendText implements [encoding.TextAppender]. The output
// matches that of calling the [Regexp.String] method.
//
// Note that the output is lossy in some cases: This method does not indicate
// POSIX regular expressions (i.e. those compiled by calling [CompilePOSIX]), or
// those for which the [Regexp.Longest] method has been called.
func (re *Regexp) AppendText(b []byte) ([]byte, error) {
	return append(b, re.String()...), nil
}

// MarshalText implements [encoding.TextMarshaler]. The output
// matches that of calling the [Regexp.AppendText] method.
//
// See [Regexp.AppendText] for more information.
func (re *Regexp) MarshalText() ([]byte, error) {
	return re.AppendText(nil)
}

// UnmarshalText implements [encoding.TextUnmarshaler] by calling
// [Compile] on the encoded value.
func (re *Regexp) UnmarshalText(text []byte) error {
	newRE, err := Compile(string(text))
	if err != nil {
		return err
	}
	*re = *newRE
	return nil
}