package matching
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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.
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.
Usage
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
Regexrepresents a compiled regular expression pattern. Since compilation is expensive, frequently usedRegexes should be constructed once, outside of loops and perhaps in a companion object.The canonical way to create a
Regexis by using the methodr, provided implicitly for strings:val date = raw"(\d{4})-(\d{2})-(\d{2})".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""". The same result is achieved with certain interpolators, such asraw"\d".ror a custom interpolatorr"\d"that also compiles theRegex.Extraction
To extract the capturing groups when a
Regexis matched, use it as an extractor in a pattern match:"2004-01-20" match { case date(year, month, day) => s"$year was a good year for PLs." }
To check only whether the
Regexmatches, ignoring any groups, use a sequence wildcard:"2004-01-20" match { case date(_*) => "It's a date!" }
That works because a
Regexextractor produces a sequence of strings. Extracting only the year from a date could also be expressed with a sequence wildcard:"2004-01-20" match { case date(year, _*) => s"$year was a good year for PLs." }
In a pattern match,
Regexnormally matches the entire input. However, an unanchoredRegexfinds 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." }
Find Matches
To find or replace matches of the pattern, use the various find and replace methods. For each method, there is a version for working with matched strings and another for working with
Matchobjects.For example, pattern matching with an unanchored
Regex, as in the previous example, can also be accomplished usingfindFirstMatchIn. ThefindFirstmethods return anOptionwhich is non-empty if a match is found, orNonefor 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)
To iterate over the matched strings, use
findAllIn, which returns a special iterator that can be queried for theMatchDataof the last match:val mi = date.findAllIn(dates) while (mi.hasNext) { val d = mi.next if (mi.group(1).toInt < 1960) println(s"$d: An oldie but goodie.") }
Although the
MatchIteratorreturned byfindAllInis used like anyIterator, with alternating calls tohasNextandnext,hasNexthas the additional side effect of advancing the underlying matcher to the next unconsumed match. This effect is visible in theMatchDatarepresenting the "current match".val r = "(ab+c)".r val s = "xxxabcyyyabbczzz" r.findAllIn(s).start // 3 val mi = r.findAllIn(s) mi.hasNext // true mi.start // 3 mi.next() // "abc" mi.start // 3 mi.hasNext // true mi.start // 9 mi.next() // "abbc"
The example shows that methods on
MatchDatasuch asstartwill advance to the first match, if necessary. It also shows thathasNextwill advance to the next unconsumed match, ifnexthas already returned the current match.The current
MatchDatacan be captured using thematchDatamethod. Alternatively,findAllMatchInreturns anIterator[Match], where there is no interaction between the iterator andMatchobjects it has already produced.Note that
findAllInfinds matches that don't overlap. (See findAllIn for more examples.)val num = raw"(\d+)".r val all = num.findAllIn("123").toList // List("123"), not List("123", "23", "3")
Replace Text
Text replacement can be performed unconditionally or as a function of the current match:
val redacted = date.replaceAllIn(dates, "XXXX-XX-XX") val yearsOnly = date.replaceAllIn(dates, m => m.group(1)) val months = (0 to 11).map { i => val c = Calendar.getInstance; c.set(2014, i, 1); f"$c%tb" } val reformatted = date.replaceAllIn(dates, _ match { case date(y,m,d) => f"${months(m.toInt - 1)} $d, $y" })
Pattern matching the
Matchagainst theRegexthat created it does not reapply theRegex. In the expression forreformatted, eachdatematch is computed once. But it is possible to apply aRegexto aMatchresulting 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" })
- Annotations
- @SerialVersionUID()
- Version
1.1, 29/01/2008
- See also
java.util.regex.Pattern
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trait
UnanchoredRegex extends Regex
A Regex that finds the first match when used in a pattern match.
A Regex that finds the first match when used in a pattern match.
- See also
Value Members
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object
Regex extends Serializable
This object defines inner classes that describe regex matches and helper objects.
This is the documentation for the Scala standard library.
Package structure
The scala package contains core types like
Int,Float,ArrayorOptionwhich are accessible in all Scala compilation units without explicit qualification or imports.Notable packages include:
scala.collectionand its sub-packages contain Scala's collections frameworkscala.collection.immutable- Immutable, sequential data-structures such asVector,List,Range,HashMaporHashSetscala.collection.mutable- Mutable, sequential data-structures such asArrayBuffer,StringBuilder,HashMaporHashSetscala.collection.concurrent- Mutable, concurrent data-structures such asTrieMapscala.collection.parallel.immutable- Immutable, parallel data-structures such asParVector,ParRange,ParHashMaporParHashSetscala.collection.parallel.mutable- Mutable, parallel data-structures such asParArray,ParHashMap,ParTrieMaporParHashSetscala.concurrent- Primitives for concurrent programming such asFuturesandPromisesscala.io- Input and output operationsscala.math- Basic math functions and additional numeric types likeBigIntandBigDecimalscala.sys- Interaction with other processes and the operating systemscala.util.matching- Regular expressionsOther packages exist. See the complete list on the right.
Additional parts of the standard library are shipped as separate libraries. These include:
scala.reflect- Scala's reflection API (scala-reflect.jar)scala.xml- XML parsing, manipulation, and serialization (scala-xml.jar)scala.swing- A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)scala.util.parsing- Parser combinators (scala-parser-combinators.jar)Automatic imports
Identifiers in the scala package and the
scala.Predefobject are always in scope by default.Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example,
Listis an alias forscala.collection.immutable.List.Other aliases refer to classes provided by the underlying platform. For example, on the JVM,
Stringis an alias forjava.lang.String.