Matching against a regular expression in Scala

Question

I fairly frequently match strings against regular expressions. In Java:

java.util.regex.Pattern.compile("\w+").matcher("this_is").matches

Ouch. Scala has many alternatives.

1. "\\w+".r.pattern.matcher("this_is").matches
2. "this_is".matches("\\w+")
3. "\\w+".r unapplySeq "this_is" isDefined
4. val R = "\\w+".r; "this_is" match { case R() => true; case _ => false}

The first is just as heavy-weight as the Java code.

The problem with the second is that you can't supply a compiled pattern ("this_is".matches("\\w+".r")). (This seems to be an anti-pattern since almost every time there is a method that takes a regex to compile there is an overload that takes a regex).

The problem with the third is that it abuses unapplySeq and thus is cryptic.

The fourth is great when decomposing parts of a regular expression, but is too heavy-weight when you only want a boolean result.

Am I missing an easy way to check for matches against a regular expression? Is there a reason why String#matches(regex: Regex): Boolean is not defined? In fact, where is String#matches(uncompiled: String): Boolean defined?

Answer 1

You can define a pattern like this :

scala> val Email = """(\w+)@([\w\.]+)""".r 

findFirstIn will return Some[String] if it matches or else None.

scala> Email.findFirstIn("[email protected]") res1: Option[String] = Some([email protected])  scala> Email.findFirstIn("test") rest2: Option[String] = None 

You could even extract :

scala> val Email(name, domain) = "[email protected]" name: String = test domain: String = example.com 

Finally, you can also use conventional String.matches method (and even recycle the previously defined Email Regexp :

scala> "[email protected]".matches(Email.toString) res6: Boolean = true 

Hope this will help.

Answer 2

I created a little "Pimp my Library" pattern for that problem. Maybe it'll help you out.

import util.matching.Regex  object RegexUtils {   class RichRegex(self: Regex) {     def =~(s: String) = self.pattern.matcher(s).matches   }   implicit def regexToRichRegex(r: Regex) = new RichRegex(r) } 

Example of use

scala> import RegexUtils._ scala> """\w+""".r =~ "foo" res12: Boolean = true