scala.util.matching.Regex

class Regex extends Serializable

A regular expression is used to determine whether a string matches a pattern and, if it does, to extract or transform the parts that match.

This class delegates to the java.util.regex package of the Java Platform. See the documentation for java.util.regex.Pattern for details about the regular expression syntax for pattern strings.

An instance of Regex represents a compiled regular expression pattern. Since compilation is expensive, frequently used Regex es should be constructed once, outside of loops and perhaps in a companion object.

The canonical way to create a Regex is by using the method r , provided implicitly for strings:

val date = """(\d\d\d\d)-(\d\d)-(\d\d)""".r

Since escapes are not processed in multi-line string literals, using triple quotes avoids having to escape the backslash character, so that "\\d" can be written """\d""" .

To extract the capturing groups when a Regex is matched, use it as an extractor in a pattern match:

"2004-01-20" match {
  case date(year, month, day) => s"$year was a good year for PLs."
}

To check only whether the Regex matches, ignoring any groups, use a sequence wildcard:

"2004-01-20" match {
  case date(_*) => "It's a date!"
}

That works because a Regex extractor produces a sequence of strings. Extracting only the year from a date could also be expressed with a sequence wildcard:

"2004-01-20" match {
  case date(year, _*) => s"$year was a good year for PLs."
}

In a pattern match, Regex normally matches the entire input. However, an unanchored Regex finds the pattern anywhere in the input.

val embeddedDate = date.unanchored
"Date: 2004-01-20 17:25:18 GMT (10 years, 28 weeks, 5 days, 17 hours and 51 minutes ago)" match {
  case embeddedDate("2004", "01", "20") => "A Scala is born."
}

To find or replace matches of the pattern, use the various find and replace methods. There is a flavor of each method that produces matched strings and another that produces Match objects.

For example, pattern matching with an unanchored Regex , as in the previous example, is the same as using findFirstMatchIn , except that the findFirst methods return an Option , or None for no match:

val dates = "Important dates in history: 2004-01-20, 1958-09-05, 2010-10-06, 2011-07-15"
val firstDate = date findFirstIn dates getOrElse "No date found."
val firstYear = for (m <- date findFirstMatchIn dates) yield m group 1

To find all matches:

val allYears = for (m <- date findAllMatchIn dates) yield m group 1

But findAllIn returns a special iterator of strings that can be queried for the MatchData of the last match:

val mi = date findAllIn dates
val oldies = mi filter (_ => (mi group 1).toInt < 1960) map (s => s"$s: An oldie but goodie.")

Note that findAllIn finds matches that don’t overlap. (See findAllIn for more examples.)

val num = """(\d+)""".r
val all = (num findAllIn "123").toList  // List("123"), not List("123", "23", "3")

Text replacement can be performed unconditionally or as a function of the current match:

val redacted    = date replaceAllIn (dates, "XXXX-XX-XX")
val yearsOnly   = date replaceAllIn (dates, m => m group 1)
val months      = (0 to 11) map { i => val c = Calendar.getInstance; c.set(2014, i, 1); f"$c%tb" }
val reformatted = date replaceAllIn (dates, _ match { case date(y,m,d) => f"${months(m.toInt - 1)} $d, $y" })

Pattern matching the Match against the Regex that created it does not reapply the Regex . In the expression for reformatted , each date match is computed once. But it is possible to apply a Regex to a Match resulting from a different pattern:

val docSpree = """2011(?:-\d{2}){2}""".r
val docView  = date replaceAllIn (dates, _ match {
  case docSpree() => "Historic doc spree!"
  case _          => "Something else happened"
})

Deprecated Value Members From scala.util.matching.Regex

def unapplySeq(target: Any): Option[List[String]]

Tries to match target.

  • target
    • The string to match
  • returns
    • The matches
  • Annotations
    • @ deprecated
  • Deprecated
    • (Since version 2.11.0) Extracting a match result from anything but a CharSequence or Match is deprecated

(defined at scala.util.matching.Regex)

Instance Constructors From scala.util.matching.Regex

new Regex(regex: String, groupNames: String*)

Compile a regular expression, supplied as a string, into a pattern that can be matched against inputs.

If group names are supplied, they can be used this way:

val namedDate  = new Regex("""(\d\d\d\d)-(\d\d)-(\d\d)""", "year", "month", "day")
val namedYears = for (m <- namedDate findAllMatchIn dates) yield m group "year"

This constructor does not support options as flags, which must be supplied as inline flags in the pattern string: (?idmsux-idmsux) .

  • regex
    • The regular expression to compile.
  • groupNames
    • Names of capturing groups.

(defined at scala.util.matching.Regex)

Value Members From scala.util.matching.Regex

def anchored: Regex

(defined at scala.util.matching.Regex)

def findAllIn(source: CharSequence): MatchIterator

Return all non-overlapping matches of this Regex in the given character sequence as a scala.util.matching.Regex.MatchIterator, which is a special scala.collection.Iterator that returns the matched strings but can also be queried for more data about the last match, such as capturing groups and start position.

A MatchIterator can also be converted into an iterator that returns objects of type scala.util.matching.Regex.Match, such as is normally returned by findAllMatchIn .

Where potential matches overlap, the first possible match is returned, followed by the next match that follows the input consumed by the first match:

val hat  = "hat[^a]+".r
val hathaway = "hathatthattthatttt"
val hats = (hat findAllIn hathaway).toList                     // List(hath, hattth)
val pos  = (hat findAllMatchIn hathaway map (_.start)).toList  // List(0, 7)

To return overlapping matches, it is possible to formulate a regular expression with lookahead ( ?= ) that does not consume the overlapping region.

val madhatter = "(h)(?=(at[^a]+))".r
val madhats   = (madhatter findAllMatchIn hathaway map {
  case madhatter(x,y) => s"$x$y"
}).toList                                       // List(hath, hatth, hattth, hatttt)

Attempting to retrieve match information before performing the first match or after exhausting the iterator results in java.lang.IllegalStateException. See scala.util.matching.Regex.MatchIterator for details.

  • source
    • The text to match against.
  • returns
    • A scala.util.matching.Regex.MatchIterator of matched substrings.

Example:

for (words <- """\w+""".r findAllIn "A simple example.") yield words

(defined at scala.util.matching.Regex)

def findAllMatchIn(source: CharSequence): Iterator[Match]

Return all non-overlapping matches of this regexp in given character sequence as a scala.collection.Iterator of scala.util.matching.Regex.Match.

  • source
    • The text to match against.
  • returns
    • A scala.collection.Iterator of scala.util.matching.Regex.Match for all matches.

Example:

for (words <- """\w+""".r findAllMatchIn "A simple example.") yield words.start

(defined at scala.util.matching.Regex)

def findFirstIn(source: CharSequence): Option[String]

Return an optional first matching string of this Regex in the given character sequence, or None if there is no match.

  • source
    • The text to match against.
  • returns
    • An scala.Option of the first matching string in the text.

Example:

"""\w+""".r findFirstIn "A simple example." foreach println // prints "A"

(defined at scala.util.matching.Regex)

def findFirstMatchIn(source: CharSequence): Option[Match]

Return an optional first match of this Regex in the given character sequence, or None if it does not exist.

If the match is successful, the scala.util.matching.Regex.Match can be queried for more data.

  • source
    • The text to match against.
  • returns
    • A scala.Option of scala.util.matching.Regex.Match of the first matching string in the text.

Example:

("""[a-z]""".r findFirstMatchIn "A simple example.") map (_.start) // returns Some(2), the index of the first match in the text

(defined at scala.util.matching.Regex)

def findPrefixMatchOf(source: CharSequence): Option[Match]

Return an optional match of this Regex at the beginning of the given character sequence, or None if it matches no prefix of the character sequence.

Unlike findFirstMatchIn , this method will only return a match at the beginning of the input.

  • source
    • The text to match against.
  • returns
    • A scala.Option of the scala.util.matching.Regex.Match of the matched string.

Example:

"""\w+""".r findPrefixMatchOf "A simple example." map (_.after) // returns Some(" simple example.")

(defined at scala.util.matching.Regex)

def findPrefixOf(source: CharSequence): Option[String]

Return an optional match of this Regex at the beginning of the given character sequence, or None if it matches no prefix of the character sequence.

Unlike findFirstIn , this method will only return a match at the beginning of the input.

  • source
    • The text to match against.
  • returns
    • A scala.Option of the matched prefix.

Example:

"""\p{Lower}""".r findPrefixOf "A simple example." // returns None, since the text does not begin with a lowercase letter

(defined at scala.util.matching.Regex)

val pattern: Pattern

The compiled pattern

(defined at scala.util.matching.Regex)

def replaceAllIn(target: CharSequence, replacer: (Match) ⇒ String): String

Replaces all matches using a replacer function. The replacer function takes a scala.util.matching.Regex.Match so that extra information can be obtained from the match. For example:

import scala.util.matching.Regex
val datePattern = new Regex("""(\d\d\d\d)-(\d\d)-(\d\d)""", "year", "month", "day")
val text = "From 2011-07-15 to 2011-07-17"
val repl = datePattern replaceAllIn (text, m => s"${m group "month"}/${m group "day"}")

In the replacement String, a dollar sign ( $ ) followed by a number will be interpreted as a reference to a group in the matched pattern, with numbers 1 through 9 corresponding to the first nine groups, and 0 standing for the whole match. Any other character is an error. The backslash ( \ ) character will be interpreted as an escape character and can be used to escape the dollar sign. Use Regex.quoteReplacement to escape these characters.

  • target
    • The string to match.
  • replacer
    • The function which maps a match to another string.
  • returns
    • The target string after replacements.

(defined at scala.util.matching.Regex)

def replaceAllIn(target: CharSequence, replacement: String): String

Replaces all matches by a string.

In the replacement String, a dollar sign ( $ ) followed by a number will be interpreted as a reference to a group in the matched pattern, with numbers 1 through 9 corresponding to the first nine groups, and 0 standing for the whole match. Any other character is an error. The backslash ( \ ) character will be interpreted as an escape character and can be used to escape the dollar sign. Use Regex.quoteReplacement to escape these characters.

  • target
    • The string to match
  • replacement
    • The string that will replace each match
  • returns
    • The resulting string

Example:

"""\d+""".r replaceAllIn ("July 15", "") // returns "July "

(defined at scala.util.matching.Regex)

def replaceFirstIn(target: CharSequence, replacement: String): String

Replaces the first match by a string.

In the replacement String, a dollar sign ( $ ) followed by a number will be interpreted as a reference to a group in the matched pattern, with numbers 1 through 9 corresponding to the first nine groups, and 0 standing for the whole match. Any other character is an error. The backslash ( \ ) character will be interpreted as an escape character and can be used to escape the dollar sign. Use Regex.quoteReplacement to escape these characters.

  • target
    • The string to match
  • replacement
    • The string that will replace the match
  • returns
    • The resulting string

(defined at scala.util.matching.Regex)

def replaceSomeIn(target: CharSequence, replacer: (Match) ⇒ Option[String]): String

Replaces some of the matches using a replacer function that returns an scala.Option. The replacer function takes a scala.util.matching.Regex.Match so that extra information can be obtained from the match. For example:

import scala.util.matching.Regex._

val vars = Map("x" -> "a var", "y" -> """some $ and \ signs""")
val text = "A text with variables %x, %y and %z."
val varPattern = """%(\w+)""".r
val mapper = (m: Match) => vars get (m group 1) map (quoteReplacement(_))
val repl = varPattern replaceSomeIn (text, mapper)

In the replacement String, a dollar sign ( $ ) followed by a number will be interpreted as a reference to a group in the matched pattern, with numbers 1 through 9 corresponding to the first nine groups, and 0 standing for the whole match. Any other character is an error. The backslash ( \ ) character will be interpreted as an escape character and can be used to escape the dollar sign. Use Regex.quoteReplacement to escape these characters.

  • target
    • The string to match.
  • replacer
    • The function which optionally maps a match to another string.
  • returns
    • The target string after replacements.

(defined at scala.util.matching.Regex)

def runMatcher(m: Matcher): Boolean

  • Attributes
    • protected

(defined at scala.util.matching.Regex)

def split(toSplit: CharSequence): Array[String]

Splits the provided character sequence around matches of this regexp.

  • toSplit
    • The character sequence to split
  • returns
    • The array of strings computed by splitting the input around matches of this regexp

(defined at scala.util.matching.Regex)

def unanchored: UnanchoredRegex

Create a new Regex with the same pattern, but no requirement that the entire String matches in extractor patterns.

Normally, matching on date behaves as though the pattern were enclosed in anchors, "^pattern$".

The unanchored Regex behaves as though those anchors were removed.

Note that this method does not actually strip any matchers from the pattern.

Calling anchored returns the original Regex .

val date = """(\d\d\d\d)-(\d\d)-(\d\d)""".r.unanchored

val date(year, month, day) = "Date 2011-07-15"                       // OK

val copyright: String = "Date of this document: 2011-07-15" match {
  case date(year, month, day) => s"Copyright $year"                  // OK
  case _                      => "No copyright"
}
  • returns
    • The new unanchored regex

(defined at scala.util.matching.Regex)

def unapplySeq(c: Char): Option[List[Char]]

Tries to match the String representation of a scala.Char.

If the match succeeds, the result is the first matching group if any groups are defined, or an empty Sequence otherwise.

For example:

val cat = "cat"
// the case must consume the group to match
val r = """(\p{Lower})""".r
cat(0) match { case r(x) => true }
cat(0) match { case r(_) => true }
cat(0) match { case r(_*) => true }
cat(0) match { case r() => true }     // no match

// there is no group to extract
val r = """\p{Lower}""".r
cat(0) match { case r(x) => true }    // no match
cat(0) match { case r(_) => true }    // no match
cat(0) match { case r(_*) => true }   // matches
cat(0) match { case r() => true }     // matches

// even if there are multiple groups, only one is returned
val r = """((.))""".r
cat(0) match { case r(_) => true }    // matches
cat(0) match { case r(_,_) => true }  // no match
  • c
    • The Char to match
  • returns
    • The match

(defined at scala.util.matching.Regex)

def unapplySeq(s: CharSequence): Option[List[String]]

Tries to match a java.lang.CharSequence.

If the match succeeds, the result is a list of the matching groups (or a null element if a group did not match any input). If the pattern specifies no groups, then the result will be an empty list on a successful match.

This method attempts to match the entire input by default; to find the next matching subsequence, use an unanchored Regex .

For example:

val p1 = "ab*c".r
val p1Matches = "abbbc" match {
  case p1() => true               // no groups
  case _    => false
}
val p2 = "a(b*)c".r
val p2Matches = "abbbc" match {
  case p2(_*) => true             // any groups
  case _      => false
}
val numberOfB = "abbbc" match {
  case p2(b) => Some(b.length)    // one group
  case _     => None
}
val p3 = "b*".r.unanchored
val p3Matches = "abbbc" match {
  case p3() => true               // find the b's
  case _    => false
}
val p4 = "a(b*)(c+)".r
val p4Matches = "abbbcc" match {
  case p4(_*) => true             // multiple groups
  case _      => false
}
val allGroups = "abbbcc" match {
  case p4(all @ _*) => all mkString "/" // "bbb/cc"
  case _            => ""
}
val cGroup = "abbbcc" match {
  case p4(_, c) => c
  case _        => ""
}
  • s
    • The string to match
  • returns
    • The matches

(defined at scala.util.matching.Regex)

def unapplySeq(m: Match): Option[List[String]]

Tries to match on a scala.util.matching.Regex.Match.

A previously failed match results in None.

If a successful match was made against the current pattern, then that result is used.

Otherwise, this Regex is applied to the previously matched input, and the result of that match is used. (defined at scala.util.matching.Regex)

Full Source:

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2007-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

/**
 * This package is concerned with regular expression (regex) matching against strings,
 * with the main goal of pulling out information from those matches, or replacing
 * them with something else.
 *
 * There are four classes and three objects, with most of them being members of
 * Regex companion object. [[scala.util.matching.Regex]] is the class users instantiate
 * to do regular expression matching.
 *
 * The remaining classes and objects in the package are used in the following way:
 *
 * * The companion object to [[scala.util.matching.Regex]] just contains the other members.
 * * [[scala.util.matching.Regex.Match]] makes more information about a match available.
 * * [[scala.util.matching.Regex.MatchIterator]] is used to iterate over multiple matches.
 * * [[scala.util.matching.Regex.MatchData]] is just a base trait for the above classes.
 * * [[scala.util.matching.Regex.Groups]] extracts group from a [[scala.util.matching.Regex.Match]]
 *   without recomputing the match.
 * * [[scala.util.matching.Regex.Match]] converts a [[scala.util.matching.Regex.Match]]
 *   into a [[java.lang.String]].
 *
 */
package scala.util.matching

import scala.collection.AbstractIterator
import java.util.regex.{ Pattern, Matcher }

/** A regular expression is used to determine whether a string matches a pattern
 *  and, if it does, to extract or transform the parts that match.
 *
 *  This class delegates to the [[java.util.regex]] package of the Java Platform.
 *  See the documentation for [[java.util.regex.Pattern]] for details about
 *  the regular expression syntax for pattern strings.
 *
 *  An instance of `Regex` represents a compiled regular expression pattern.
 *  Since compilation is expensive, frequently used `Regex`es should be constructed
 *  once, outside of loops and perhaps in a companion object.
 *
 *  The canonical way to create a `Regex` is by using the method `r`, provided
 *  implicitly for strings:
 *
 *  {{{
 *  val date = """(\d\d\d\d)-(\d\d)-(\d\d)""".r
 *  }}}
 *
 *  Since escapes are not processed in multi-line string literals, using triple quotes
 *  avoids having to escape the backslash character, so that `"\\d"` can be written `"""\d"""`.
 *
 *  To extract the capturing groups when a `Regex` is matched, use it as
 *  an extractor in a pattern match:
 *
 *  {{{
 *  "2004-01-20" match {
 *    case date(year, month, day) => s"$year was a good year for PLs."
 *  }
 *  }}}
 *
 *  To check only whether the `Regex` matches, ignoring any groups,
 *  use a sequence wildcard:
 *
 *  {{{
 *  "2004-01-20" match {
 *    case date(_*) => "It's a date!"
 *  }
 *  }}}
 *
 *  That works because a `Regex` extractor produces a sequence of strings.
 *  Extracting only the year from a date could also be expressed with
 *  a sequence wildcard:
 *
 *  {{{
 *  "2004-01-20" match {
 *    case date(year, _*) => s"$year was a good year for PLs."
 *  }
 *  }}}
 *
 *  In a pattern match, `Regex` normally matches the entire input.
 *  However, an unanchored `Regex` finds the pattern anywhere
 *  in the input.
 *
 *  {{{
 *  val embeddedDate = date.unanchored
 *  "Date: 2004-01-20 17:25:18 GMT (10 years, 28 weeks, 5 days, 17 hours and 51 minutes ago)" match {
 *    case embeddedDate("2004", "01", "20") => "A Scala is born."
 *  }
 *  }}}
 *
 *  To find or replace matches of the pattern, use the various find and replace methods.
 *  There is a flavor of each method that produces matched strings and
 *  another that produces `Match` objects.
 *
 *  For example, pattern matching with an unanchored `Regex`, as in the previous example,
 *  is the same as using `findFirstMatchIn`, except that the findFirst methods return an `Option`,
 *  or `None` for no match:
 *
 *  {{{
 *  val dates = "Important dates in history: 2004-01-20, 1958-09-05, 2010-10-06, 2011-07-15"
 *  val firstDate = date findFirstIn dates getOrElse "No date found."
 *  val firstYear = for (m <- date findFirstMatchIn dates) yield m group 1
 *  }}}
 *
 *  To find all matches:
 *
 *  {{{
 *  val allYears = for (m <- date findAllMatchIn dates) yield m group 1
 *  }}}
 *
 *  But `findAllIn` returns a special iterator of strings that can be queried for the `MatchData`
 *  of the last match:
 *
 *  {{{
 *  val mi = date findAllIn dates
 *  val oldies = mi filter (_ => (mi group 1).toInt < 1960) map (s => s"$s: An oldie but goodie.")
 *  }}}
 *
 *  Note that `findAllIn` finds matches that don't overlap. (See [[findAllIn]] for more examples.)
 *
 *  {{{
 *  val num = """(\d+)""".r
 *  val all = (num findAllIn "123").toList  // List("123"), not List("123", "23", "3")
 *  }}}
 *
 *  Text replacement can be performed unconditionally or as a function of the current match:
 *
 *  {{{
 *  val redacted    = date replaceAllIn (dates, "XXXX-XX-XX")
 *  val yearsOnly   = date replaceAllIn (dates, m => m group 1)
 *  val months      = (0 to 11) map { i => val c = Calendar.getInstance; c.set(2014, i, 1); f"$c%tb" }
 *  val reformatted = date replaceAllIn (dates, _ match { case date(y,m,d) => f"${months(m.toInt - 1)} $d, $y" })
 *  }}}
 *
 *  Pattern matching the `Match` against the `Regex` that created it does not reapply the `Regex`.
 *  In the expression for `reformatted`, each `date` match is computed once. But it is possible to apply a
 *  `Regex` to a `Match` resulting from a different pattern:
 *
 *  {{{
 *  val docSpree = """2011(?:-\d{2}){2}""".r
 *  val docView  = date replaceAllIn (dates, _ match {
 *    case docSpree() => "Historic doc spree!"
 *    case _          => "Something else happened"
 *  })
 *  }}}
 *
 *  @see [[java.util.regex.Pattern]]
 *
 *  @author  Thibaud Hottelier
 *  @author  Philipp Haller
 *  @author  Martin Odersky
 *  @version 1.1, 29/01/2008
 *
 *  @param pattern    The compiled pattern
 *  @param groupNames A mapping from names to indices in capture groups
 *
 *  @define replacementString
 *  In the replacement String, a dollar sign (`$`) followed by a number will be
 *  interpreted as a reference to a group in the matched pattern, with numbers
 *  1 through 9 corresponding to the first nine groups, and 0 standing for the
 *  whole match. Any other character is an error. The backslash (`\`) character
 *  will be interpreted as an escape character and can be used to escape the
 *  dollar sign. Use `Regex.quoteReplacement` to escape these characters.
 */
@SerialVersionUID(-2094783597747625537L)
class Regex private[matching](val pattern: Pattern, groupNames: String*) extends Serializable {
  outer =>

  import Regex._

  /** Compile a regular expression, supplied as a string, into a pattern that
   *  can be matched against inputs.
   *
   *  If group names are supplied, they can be used this way:
   *
   *  {{{
   *  val namedDate  = new Regex("""(\d\d\d\d)-(\d\d)-(\d\d)""", "year", "month", "day")
   *  val namedYears = for (m <- namedDate findAllMatchIn dates) yield m group "year"
   *  }}}
   *
   *  This constructor does not support options as flags, which must be
   *  supplied as inline flags in the pattern string: `(?idmsux-idmsux)`.
   *
   *  @param regex      The regular expression to compile.
   *  @param groupNames Names of capturing groups.
   */
  def this(regex: String, groupNames: String*) = this(Pattern.compile(regex), groupNames: _*)

  /** Tries to match a [[java.lang.CharSequence]].
   *
   *  If the match succeeds, the result is a list of the matching
   *  groups (or a `null` element if a group did not match any input).
   *  If the pattern specifies no groups, then the result will be an empty list
   *  on a successful match.
   *
   *  This method attempts to match the entire input by default; to find the next
   *  matching subsequence, use an unanchored `Regex`.
   *
   *  For example:
   *
   *  {{{
   *  val p1 = "ab*c".r
   *  val p1Matches = "abbbc" match {
   *    case p1() => true               // no groups
   *    case _    => false
   *  }
   *  val p2 = "a(b*)c".r
   *  val p2Matches = "abbbc" match {
   *    case p2(_*) => true             // any groups
   *    case _      => false
   *  }
   *  val numberOfB = "abbbc" match {
   *    case p2(b) => Some(b.length)    // one group
   *    case _     => None
   *  }
   *  val p3 = "b*".r.unanchored
   *  val p3Matches = "abbbc" match {
   *    case p3() => true               // find the b's
   *    case _    => false
   *  }
   *  val p4 = "a(b*)(c+)".r
   *  val p4Matches = "abbbcc" match {
   *    case p4(_*) => true             // multiple groups
   *    case _      => false
   *  }
   *  val allGroups = "abbbcc" match {
   *    case p4(all @ _*) => all mkString "/" // "bbb/cc"
   *    case _            => ""
   *  }
   *  val cGroup = "abbbcc" match {
   *    case p4(_, c) => c
   *    case _        => ""
   *  }
   *  }}}
   *
   *  @param  s     The string to match
   *  @return       The matches
   */
  def unapplySeq(s: CharSequence): Option[List[String]] = s match {
    case null => None
    case _    =>
      val m = pattern matcher s
      if (runMatcher(m)) Some((1 to m.groupCount).toList map m.group)
      else None
  }

  /** Tries to match the String representation of a [[scala.Char]].
   *
   *  If the match succeeds, the result is the first matching
   *  group if any groups are defined, or an empty Sequence otherwise.
   *
   *  For example:
   *
   *  {{{
   *  val cat = "cat"
   *  // the case must consume the group to match
   *  val r = """(\p{Lower})""".r
   *  cat(0) match { case r(x) => true }
   *  cat(0) match { case r(_) => true }
   *  cat(0) match { case r(_*) => true }
   *  cat(0) match { case r() => true }     // no match
   *
   *  // there is no group to extract
   *  val r = """\p{Lower}""".r
   *  cat(0) match { case r(x) => true }    // no match
   *  cat(0) match { case r(_) => true }    // no match
   *  cat(0) match { case r(_*) => true }   // matches
   *  cat(0) match { case r() => true }     // matches
   *
   *  // even if there are multiple groups, only one is returned
   *  val r = """((.))""".r
   *  cat(0) match { case r(_) => true }    // matches
   *  cat(0) match { case r(_,_) => true }  // no match
   *  }}}
   *
   *  @param  c     The Char to match
   *  @return       The match
   */
  def unapplySeq(c: Char): Option[List[Char]] = {
    val m = pattern matcher c.toString
    if (runMatcher(m)) {
      if (m.groupCount > 0) Some((m group 1).toList) else Some(Nil)
    } else None
  }

  /** Tries to match on a [[scala.util.matching.Regex.Match]].
   *
   *  A previously failed match results in None.
   *
   *  If a successful match was made against the current pattern, then that result is used.
   *
   *  Otherwise, this Regex is applied to the previously matched input,
   *  and the result of that match is used.
   */
  def unapplySeq(m: Match): Option[List[String]] =
    if (m == null || m.matched == null) None
    else if (m.matcher.pattern == this.pattern) Some((1 to m.groupCount).toList map m.group)
    else unapplySeq(m.matched)

  /** Tries to match target.
   *  @param target The string to match
   *  @return       The matches
   */
  @deprecated("Extracting a match result from anything but a CharSequence or Match is deprecated", "2.11.0")
  def unapplySeq(target: Any): Option[List[String]] = target match {
    case s: CharSequence =>
      val m = pattern matcher s
      if (runMatcher(m)) Some((1 to m.groupCount).toList map m.group)
      else None
    case m: Match => unapplySeq(m.matched)
    case _ => None
  }

  //  @see UnanchoredRegex
  protected def runMatcher(m: Matcher) = m.matches()

  /** Return all non-overlapping matches of this `Regex` in the given character 
   *  sequence as a [[scala.util.matching.Regex.MatchIterator]],
   *  which is a special [[scala.collection.Iterator]] that returns the
   *  matched strings but can also be queried for more data about the last match,
   *  such as capturing groups and start position.
   * 
   *  A `MatchIterator` can also be converted into an iterator
   *  that returns objects of type [[scala.util.matching.Regex.Match]],
   *  such as is normally returned by `findAllMatchIn`.
   * 
   *  Where potential matches overlap, the first possible match is returned,
   *  followed by the next match that follows the input consumed by the
   *  first match:
   *
   *  {{{
   *  val hat  = "hat[^a]+".r
   *  val hathaway = "hathatthattthatttt"
   *  val hats = (hat findAllIn hathaway).toList                     // List(hath, hattth)
   *  val pos  = (hat findAllMatchIn hathaway map (_.start)).toList  // List(0, 7)
   *  }}}
   *
   *  To return overlapping matches, it is possible to formulate a regular expression
   *  with lookahead (`?=`) that does not consume the overlapping region.
   *
   *  {{{
   *  val madhatter = "(h)(?=(at[^a]+))".r
   *  val madhats   = (madhatter findAllMatchIn hathaway map {
   *    case madhatter(x,y) => s"$x$y"
   *  }).toList                                       // List(hath, hatth, hattth, hatttt)
   *  }}}
   *
   *  Attempting to retrieve match information before performing the first match
   *  or after exhausting the iterator results in [[java.lang.IllegalStateException]].
   *  See [[scala.util.matching.Regex.MatchIterator]] for details.
   *
   *  @param source The text to match against.
   *  @return       A [[scala.util.matching.Regex.MatchIterator]] of matched substrings.
   *  @example      {{{for (words <- """\w+""".r findAllIn "A simple example.") yield words}}}
   */
  def findAllIn(source: CharSequence) = new Regex.MatchIterator(source, this, groupNames)

  /** Return all non-overlapping matches of this regexp in given character sequence as a
   *  [[scala.collection.Iterator]] of [[scala.util.matching.Regex.Match]].
   *
   *  @param source The text to match against.
   *  @return       A [[scala.collection.Iterator]] of [[scala.util.matching.Regex.Match]] for all matches.
   *  @example      {{{for (words <- """\w+""".r findAllMatchIn "A simple example.") yield words.start}}}
   */
  def findAllMatchIn(source: CharSequence): Iterator[Match] = {
    val matchIterator = findAllIn(source)
    new Iterator[Match] {
      def hasNext = matchIterator.hasNext
      def next: Match = {
        matchIterator.next()
        new Match(matchIterator.source, matchIterator.matcher, matchIterator.groupNames).force
      }
    }
  }

  /** Return an optional first matching string of this `Regex` in the given character sequence,
   *  or None if there is no match.
   *
   *  @param source The text to match against.
   *  @return       An [[scala.Option]] of the first matching string in the text.
   *  @example      {{{"""\w+""".r findFirstIn "A simple example." foreach println // prints "A"}}}
   */
  def findFirstIn(source: CharSequence): Option[String] = {
    val m = pattern.matcher(source)
    if (m.find) Some(m.group) else None
  }

  /** Return an optional first match of this `Regex` in the given character sequence,
   *  or None if it does not exist.
   *
   *  If the match is successful, the [[scala.util.matching.Regex.Match]] can be queried for
   *  more data.
   *
   *  @param source The text to match against.
   *  @return       A [[scala.Option]] of [[scala.util.matching.Regex.Match]] of the first matching string in the text.
   *  @example      {{{("""[a-z]""".r findFirstMatchIn "A simple example.") map (_.start) // returns Some(2), the index of the first match in the text}}}
   */
  def findFirstMatchIn(source: CharSequence): Option[Match] = {
    val m = pattern.matcher(source)
    if (m.find) Some(new Match(source, m, groupNames)) else None
  }

  /** Return an optional match of this `Regex` at the beginning of the
   *  given character sequence, or None if it matches no prefix
   *  of the character sequence.
   *
   *  Unlike `findFirstIn`, this method will only return a match at
   *  the beginning of the input.
   *
   *  @param source The text to match against.
   *  @return       A [[scala.Option]] of the matched prefix.
   *  @example      {{{"""\p{Lower}""".r findPrefixOf "A simple example." // returns None, since the text does not begin with a lowercase letter}}}
   */
  def findPrefixOf(source: CharSequence): Option[String] = {
    val m = pattern.matcher(source)
    if (m.lookingAt) Some(m.group) else None
  }

  /** Return an optional match of this `Regex` at the beginning of the
   *  given character sequence, or None if it matches no prefix
   *  of the character sequence.
   *
   *  Unlike `findFirstMatchIn`, this method will only return a match at
   *  the beginning of the input.
   *
   *  @param source The text to match against.
   *  @return       A [[scala.Option]] of the [[scala.util.matching.Regex.Match]] of the matched string.
   *  @example      {{{"""\w+""".r findPrefixMatchOf "A simple example." map (_.after) // returns Some(" simple example.")}}}
   */
  def findPrefixMatchOf(source: CharSequence): Option[Match] = {
    val m = pattern.matcher(source)
    if (m.lookingAt) Some(new Match(source, m, groupNames)) else None
  }

  /** Replaces all matches by a string.
   *
   *  $replacementString
   *
   *  @param target      The string to match
   *  @param replacement The string that will replace each match
   *  @return            The resulting string
   *  @example           {{{"""\d+""".r replaceAllIn ("July 15", "<NUMBER>") // returns "July <NUMBER>"}}}
   */
  def replaceAllIn(target: CharSequence, replacement: String): String = {
    val m = pattern.matcher(target)
    m.replaceAll(replacement)
  }

  /**
   * Replaces all matches using a replacer function. The replacer function takes a
   * [[scala.util.matching.Regex.Match]] so that extra information can be obtained
   * from the match. For example:
   *
   * {{{
   * import scala.util.matching.Regex
   * val datePattern = new Regex("""(\d\d\d\d)-(\d\d)-(\d\d)""", "year", "month", "day")
   * val text = "From 2011-07-15 to 2011-07-17"
   * val repl = datePattern replaceAllIn (text, m => s"${m group "month"}/${m group "day"}")
   * }}}
   *
   * $replacementString
   *
   * @param target      The string to match.
   * @param replacer    The function which maps a match to another string.
   * @return            The target string after replacements.
   */
  def replaceAllIn(target: CharSequence, replacer: Match => String): String = {
    val it = new Regex.MatchIterator(target, this, groupNames).replacementData
    it foreach (md => it replace replacer(md))
    it.replaced
  }

  /**
   * Replaces some of the matches using a replacer function that returns an [[scala.Option]].
   * The replacer function takes a [[scala.util.matching.Regex.Match]] so that extra
   * information can be obtained from the match. For example:
   *
   * {{{
   * import scala.util.matching.Regex._
   *
   * val vars = Map("x" -> "a var", "y" -> """some $ and \ signs""")
   * val text = "A text with variables %x, %y and %z."
   * val varPattern = """%(\w+)""".r
   * val mapper = (m: Match) => vars get (m group 1) map (quoteReplacement(_))
   * val repl = varPattern replaceSomeIn (text, mapper)
   * }}}
   *
   * $replacementString
   *
   * @param target      The string to match.
   * @param replacer    The function which optionally maps a match to another string.
   * @return            The target string after replacements.
   */
  def replaceSomeIn(target: CharSequence, replacer: Match => Option[String]): String = {
    val it = new Regex.MatchIterator(target, this, groupNames).replacementData
    for (matchdata <- it ; replacement <- replacer(matchdata))
      it replace replacement

    it.replaced
  }

  /** Replaces the first match by a string.
   *
   *  $replacementString
   *
   *  @param target      The string to match
   *  @param replacement The string that will replace the match
   *  @return            The resulting string
   */
  def replaceFirstIn(target: CharSequence, replacement: String): String = {
    val m = pattern.matcher(target)
    m.replaceFirst(replacement)
  }

  /** Splits the provided character sequence around matches of this regexp.
   *
   *  @param toSplit The character sequence to split
   *  @return        The array of strings computed by splitting the
   *                 input around matches of this regexp
   */
  def split(toSplit: CharSequence): Array[String] =
    pattern.split(toSplit)

  /** Create a new Regex with the same pattern, but no requirement that
   *  the entire String matches in extractor patterns.
   *
   *  Normally, matching on `date` behaves as though the pattern were
   *  enclosed in anchors, `"^pattern$"`.
   *
   *  The unanchored `Regex` behaves as though those anchors were removed.
   *
   *  Note that this method does not actually strip any matchers from the pattern.
   *
   *  Calling `anchored` returns the original `Regex`.
   *
   *  {{{
   *  val date = """(\d\d\d\d)-(\d\d)-(\d\d)""".r.unanchored
   *
   *  val date(year, month, day) = "Date 2011-07-15"                       // OK
   *
   *  val copyright: String = "Date of this document: 2011-07-15" match {
   *    case date(year, month, day) => s"Copyright $year"                  // OK
   *    case _                      => "No copyright"
   *  }
   *  }}}
   *
   *  @return        The new unanchored regex
   */
  def unanchored: UnanchoredRegex = new Regex(pattern, groupNames: _*) with UnanchoredRegex { override def anchored = outer }
  def anchored: Regex             = this

  def regex: String = pattern.pattern

  /** The string defining the regular expression */
  override def toString = regex
}

/** A [[Regex]] that finds the first match when used in a pattern match.
 *
 *  @see [[Regex#unanchored]]
 */
trait UnanchoredRegex extends Regex {
  override protected def runMatcher(m: Matcher) = m.find()
  override def unanchored = this
}

/** This object defines inner classes that describe
 *  regex matches and helper objects.
 */
object Regex {

  /** This class provides methods to access
   *  the details of a match.
   */
  trait MatchData {

    /** The source from which the match originated */
    val source: CharSequence

    /** The names of the groups, or an empty sequence if none defined */
    val groupNames: Seq[String]

    /** The number of capturing groups in the pattern.
     *  (For a given successful match, some of those groups may not have matched any input.)
     */
    def groupCount: Int

    /** The index of the first matched character, or -1 if nothing was matched */
    def start: Int

    /** The index of the first matched character in group `i`,
     *  or -1 if nothing was matched for that group.
     */
    def start(i: Int): Int

    /** The index following the last matched character, or -1 if nothing was matched. */
    def end: Int

    /** The index following the last matched character in group `i`,
     *  or -1 if nothing was matched for that group.
     */
    def end(i: Int): Int

    /** The matched string, or `null` if nothing was matched. */
    def matched: String =
      if (start >= 0) source.subSequence(start, end).toString
      else null

    /** The matched string in group `i`,
     *  or `null` if nothing was matched.
     */
    def group(i: Int): String =
      if (start(i) >= 0) source.subSequence(start(i), end(i)).toString
      else null

    /** All capturing groups, i.e., not including group(0). */
    def subgroups: List[String] = (1 to groupCount).toList map group

    /** The char sequence before first character of match,
     *  or `null` if nothing was matched.
     */
    def before: CharSequence =
      if (start >= 0) source.subSequence(0, start)
      else null

    /** The char sequence before first character of match in group `i`,
     *  or `null` if nothing was matched for that group.
     */
    def before(i: Int): CharSequence =
      if (start(i) >= 0) source.subSequence(0, start(i))
      else null

    /** Returns char sequence after last character of match,
     *  or `null` if nothing was matched.
     */
    def after: CharSequence =
      if (end >= 0) source.subSequence(end, source.length)
      else null

    /** The char sequence after last character of match in group `i`,
     *  or `null` if nothing was matched for that group.
     */
    def after(i: Int): CharSequence =
      if (end(i) >= 0) source.subSequence(end(i), source.length)
      else null

    private lazy val nameToIndex: Map[String, Int] = Map[String, Int]() ++ ("" :: groupNames.toList).zipWithIndex

    /** Returns the group with given name.
     *
     *  @param id The group name
     *  @return   The requested group
     *  @throws   NoSuchElementException if the requested group name is not defined
     */
    def group(id: String): String = nameToIndex.get(id) match {
      case None => throw new NoSuchElementException("group name "+id+" not defined")
      case Some(index) => group(index)
    }

    /** The matched string; equivalent to `matched.toString`. */
    override def toString = matched
  }

  /** Provides information about a successful match. */
  class Match(val source: CharSequence,
              private[matching] val matcher: Matcher,
              val groupNames: Seq[String]) extends MatchData {

    /** The index of the first matched character. */
    val start = matcher.start

    /** The index following the last matched character. */
    val end = matcher.end

    /** The number of subgroups. */
    def groupCount = matcher.groupCount

    private lazy val starts: Array[Int] =
      ((0 to groupCount) map matcher.start).toArray
    private lazy val ends: Array[Int] =
      ((0 to groupCount) map matcher.end).toArray

    /** The index of the first matched character in group `i`. */
    def start(i: Int) = starts(i)

    /** The index following the last matched character in group `i`. */
    def end(i: Int) = ends(i)

    /** The match itself with matcher-dependent lazy vals forced,
     *  so that match is valid even once matcher is advanced.
     */
    def force: this.type = { starts; ends; this }
  }

  /** An extractor object for Matches, yielding the matched string.
   *
   *  This can be used to help writing replacer functions when you
   *  are not interested in match data. For example:
   *
   *  {{{
   *  import scala.util.matching.Regex.Match
   *  """\w+""".r replaceAllIn ("A simple example.", _ match { case Match(s) => s.toUpperCase })
   *  }}}
   *
   */
  object Match {
    def unapply(m: Match): Some[String] = Some(m.matched)
  }

  /** An extractor object that yields the groups in the match. Using this extractor
   *  rather than the original `Regex` ensures that the match is not recomputed.
   *
   *  {{{
   *  import scala.util.matching.Regex.Groups
   *
   *  val date = """(\d\d\d\d)-(\d\d)-(\d\d)""".r
   *  val text = "The doc spree happened on 2011-07-15."
   *  val day = date replaceAllIn(text, _ match { case Groups(_, month, day) => s"$month/$day" })
   *  }}}
   */
  object Groups {
    def unapplySeq(m: Match): Option[Seq[String]] = if (m.groupCount > 0) Some(1 to m.groupCount map m.group) else None
  }

  /** A class to step through a sequence of regex matches.
   *
   *  All methods inherited from [[scala.util.matching.Regex.MatchData]] will throw
   *  a [[java.lang.IllegalStateException]] until the matcher is initialized. The
   *  matcher can be initialized by calling `hasNext` or `next()` or causing these
   *  methods to be called, such as by invoking `toString` or iterating through
   *  the iterator's elements.
   *
   *  @see [[java.util.regex.Matcher]]
   */
  class MatchIterator(val source: CharSequence, val regex: Regex, val groupNames: Seq[String])
  extends AbstractIterator[String] with Iterator[String] with MatchData { self =>

    protected[Regex] val matcher = regex.pattern.matcher(source)
    private var nextSeen = false

    /** Is there another match? */
    def hasNext: Boolean = {
      if (!nextSeen) nextSeen = matcher.find()
      nextSeen
    }

    /** The next matched substring of `source`. */
    def next(): String = {
      if (!hasNext) throw new NoSuchElementException
      nextSeen = false
      matcher.group
    }

    override def toString = super[AbstractIterator].toString

    /** The index of the first matched character. */
    def start: Int = matcher.start

    /** The index of the first matched character in group `i`. */
    def start(i: Int): Int = matcher.start(i)

    /** The index of the last matched character. */
    def end: Int = matcher.end

    /** The index following the last matched character in group `i`. */
    def end(i: Int): Int = matcher.end(i)

    /** The number of subgroups. */
    def groupCount = matcher.groupCount

    /** Convert to an iterator that yields MatchData elements instead of Strings. */
    def matchData: Iterator[Match] = new AbstractIterator[Match] {
      def hasNext = self.hasNext
      def next = { self.next(); new Match(source, matcher, groupNames).force }
    }

    /** Convert to an iterator that yields MatchData elements instead of Strings and has replacement support. */
    private[matching] def replacementData = new AbstractIterator[Match] with Replacement {
      def matcher = self.matcher
      def hasNext = self.hasNext
      def next = { self.next(); new Match(source, matcher, groupNames).force }
    }
  }

  /**
   * A trait able to build a string with replacements assuming it has a matcher.
   * Meant to be mixed in with iterators.
   */
  private[matching] trait Replacement {
    protected def matcher: Matcher

    private val sb = new java.lang.StringBuffer

    def replaced = {
      val newsb = new java.lang.StringBuffer(sb)
      matcher.appendTail(newsb)
      newsb.toString
    }

    def replace(rs: String) = matcher.appendReplacement(sb, rs)
  }

  /** Quotes strings to be used literally in regex patterns.
   *
   *  All regex metacharacters in the input match themselves literally in the output.
   *
   *  @example {{{List("US$", "CAN$").map(Regex.quote).mkString("|").r}}}
   */
  def quote(text: String): String = Pattern quote text

  /** Quotes replacement strings to be used in replacement methods.
   *
   *  Replacement methods give special meaning to backslashes (`\`) and
   *  dollar signs (`$`) in replacement strings, so they are not treated
   *  as literals. This method escapes these characters so the resulting
   *  string can be used as a literal replacement representing the input
   *  string.
   *
   *  @param text The string one wishes to use as literal replacement.
   *  @return A string that can be used to replace matches with `text`.
   *  @example {{{"CURRENCY".r.replaceAllIn(input, Regex quoteReplacement "US$")}}}
   */
  def quoteReplacement(text: String): String = Matcher quoteReplacement text
}