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("[e-mail]")
res1: Option[String] = Some([e-mail])

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

You could even extract :

scala> val Email(name, domain) = "[e-mail]"
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> "[e-mail]".matches(Email.toString)
res6: Boolean = true

Hope this will help.