diff options
Diffstat (limited to 'scala.html.markdown')
| -rw-r--r-- | scala.html.markdown | 68 |
1 files changed, 42 insertions, 26 deletions
diff --git a/scala.html.markdown b/scala.html.markdown index 5a478f2a..61c735e3 100644 --- a/scala.html.markdown +++ b/scala.html.markdown @@ -198,8 +198,10 @@ weirdSum(2, 4) // => 16 // The return keyword exists in Scala, but it only returns from the inner-most -// def that surrounds it. It has no effect on anonymous functions. For example: -def foo(x: Int) = { +// 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 => if (z > 5) return z // This line makes z the return value of foo! @@ -405,41 +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" +} ///////////////////////////////////////////////// @@ -476,7 +492,7 @@ sSquared.reduce (_+_) // The filter function takes a predicate (a function from A -> Boolean) and // selects all elements which satisfy the predicate List(1, 2, 3) filter (_ > 2) // List(3) -case class Person(name:String, phoneNumber:String) +case class Person(name:String, age:Int) List( Person(name = "Dom", age = 23), Person(name = "Bob", age = 30) |