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-rw-r--r--scala.html.markdown64
1 files changed, 39 insertions, 25 deletions
diff --git a/scala.html.markdown b/scala.html.markdown
index 336251ba..61c735e3 100644
--- a/scala.html.markdown
+++ b/scala.html.markdown
@@ -198,8 +198,8 @@ weirdSum(2, 4) // => 16
// The return keyword exists in Scala, but it only returns from the inner-most
-// def that surrounds it.
-// WARNING: Using return in Scala is error-prone and should be avoided.
+// def that surrounds it.
+// WARNING: Using return in Scala is error-prone and should be avoided.
// It has no effect on anonymous functions. For example:
def foo(x: Int): Int = {
val anonFunc: Int => Int = { z =>
@@ -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 need breaks, fall-through does not happen.
-me match { case Person(name, number) => {
- "We matched someone : " + name + ", phone : " + number }}
-
-me match { case Person(name, number) => "Match : " + name; case _ => "Hm..." }
+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
+}
-me match { case Person("George", number) => "Match"; case _ => "Hm..." }
+val email = "(.*)@(.*)".r // Define a regex for the next example.
-me match { case Person("Kate", number) => "Match"; case _ => "Hm..." }
+// 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"
-me match { case Person("Kate", _) => "Girl"; case Person("George", _) => "Boy" }
+ // You can match by type:
+ case x: Double => "Got a Double: " + x
-val kate = Person("Kate", "1234")
+ // You can specify conditions:
+ case x: Int if x > 10000 => "Got a pretty big number!"
-kate match { case Person("Kate", _) => "Girl"; case Person("George", _) => "Boy" }
+ // 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"
-// 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
+ // You can match data structures:
+ case List(1, b, c) => s"Got a list with three elements and starts with 1: 1, $b, $c"
-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
- })
+ // You can nest patterns:
+ case List(List((1, 2,"YAY"))) => "Got a list of list of tuple"
}
-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"
+// 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"
+}
/////////////////////////////////////////////////