Rewrite the pattern matching section

This commit is contained in:
Geoff Liu 2015-01-11 15:30:12 -07:00
parent 8a2c08cc88
commit 8f29b15cda

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@ -407,41 +407,55 @@ val otherGeorge = george.copy(phoneNumber = "9876")
// 6. Pattern Matching
/////////////////////////////////////////////////
val me = Person("George", "1234")
// Pattern matching is a powerful and commonly used feature in Scala. Here's how
// you pattern match a case class. NB: Unlike other languages, Scala cases do
// not have breaks.
me match { case Person(name, number) => {
"We matched someone : " + name + ", phone : " + number }}
me match { case Person(name, number) => "Match : " + name; case _ => "Hm..." }
me match { case Person("George", number) => "Match"; case _ => "Hm..." }
me match { case Person("Kate", number) => "Match"; case _ => "Hm..." }
me match { case Person("Kate", _) => "Girl"; case Person("George", _) => "Boy" }
val kate = Person("Kate", "1234")
kate match { case Person("Kate", _) => "Girl"; case Person("George", _) => "Boy" }
// Regular expressions
val email = "(.*)@(.*)".r // Invoking r on String makes it a Regex
val serialKey = """(\d{5})-(\d{5})-(\d{5})-(\d{5})""".r // Using verbatim (multiline) syntax
val matcher = (value: String) => {
println(value match {
case email(name, domain) => s"It was an email: $name"
case serialKey(p1, p2, p3, p4) => s"Serial key: $p1, $p2, $p3, $p4"
case _ => s"No match on '$value'" // default if no match found
})
def matchPerson(person: Person): String = person match {
// Then you specify the patterns:
case Person("George", number) => "We found George! His number is " + number
case Person("Kate", number) => "We found Kate! Her number is " + number
case Person(name, number) => "We matched someone : " + name + ", phone : " + number
}
matcher("mrbean@pyahoo.com") // => "It was an email: mrbean"
matcher("nope..") // => "No match on 'nope..'"
matcher("52917") // => "No match on '52917'"
matcher("52752-16432-22178-47917") // => "Serial key: 52752, 16432, 22178, 47917"
val email = "(.*)@(.*)".r // Define a regex for the next example.
// Pattern matching might look familiar to the switch statements in the C family
// of languages, but this is much more powerful. In Scala, you can match much
// more:
def matchEverything(obj: Any): String = obj match {
// You can match values:
case "Hello world" => "Got the string Hello world"
// You can match by type:
case x: Double => "Got a Double: " + x
// You can specify conditions:
case x: Int if x > 10000 => "Got a pretty big number!"
// You can match case classes as before:
case Person(name, number) => s"Got contact info for $name!"
// You can match regular expressions:
case email(name, domain) => s"Got email address $name@$domain"
// You can match tuples:
case (a: Int, b: Double, c: String) => s"Got a tuple: $a, $b, $c"
// You can match data structures:
case List(1, b, c) => s"Got a list with three elements and starts with 1: 1, $b, $c"
// You can nest patterns:
case List(List((1, 2,"YAY"))) => "Got a list of list of tuple"
}
// In fact, you can pattern match any object with an "unapply" method. This
// feature is so powerful that Scala lets you define whole functions as
// patterns:
val patternFunc: Person => String = {
case Person("George", number") => s"George's number: $number"
case Person(name, number) => s"Random person's number: $number"
}
/////////////////////////////////////////////////