diff options
Diffstat (limited to 'scala.html.markdown')
| -rw-r--r-- | scala.html.markdown | 70 |
1 files changed, 47 insertions, 23 deletions
diff --git a/scala.html.markdown b/scala.html.markdown index c482752d..745605ed 100644 --- a/scala.html.markdown +++ b/scala.html.markdown @@ -6,7 +6,6 @@ contributors: - ["Dominic Bou-Samra", "http://dbousamra.github.com"] - ["Geoff Liu", "http://geoffliu.me"] - ["Ha-Duong Nguyen", "http://reference-error.org"] -filename: learn.scala --- Scala - the scalable language @@ -43,9 +42,13 @@ Scala - the scalable language // Printing, and forcing a new line on the next print println("Hello world!") println(10) +// Hello world! +// 10 // Printing, without forcing a new line on next print print("Hello world") +print(10) +// Hello world10 // Declaring values is done using either var or val. // val declarations are immutable, whereas vars are mutable. Immutability is @@ -166,6 +169,12 @@ def sumOfSquaresShort(x: Int, y: Int): Int = x * x + y * y // Syntax for calling functions is familiar: sumOfSquares(3, 4) // => 25 +// You can use parameters names to specify them in different order +def subtract(x: Int, y: Int): Int = x - y + +subtract(10, 3) // => 7 +subtract(y=10, x=3) // => -7 + // In most cases (with recursive functions the most notable exception), function // return type can be omitted, and the same type inference we saw with variables // will work with function return values: @@ -228,7 +237,7 @@ r foreach println (5 to 1 by -1) foreach (println) -// A while loops +// A while loop var i = 0 while (i < 10) { println("i " + i); i += 1 } @@ -236,16 +245,18 @@ while (i < 10) { println("i " + i); i += 1 } // Yes, again. What happened? Why i // Show the value of i. Note that while is a loop in the classical sense - // it executes sequentially while changing the loop variable. while is very - // fast, faster that Java loops, but using the combinators and - // comprehensions above is easier to understand and parallelize + // fast, but using the combinators and comprehensions above is easier + // to understand and parallelize -// A do while loop +// A do-while loop +i = 0 do { - println("x is still less than 10") - x += 1 -} while (x < 10) + println("i is still less than 10") + i += 1 +} while (i < 10) -// Tail recursion is an idiomatic way of doing recurring things in Scala. +// Recursion is the idiomatic way of repeating an action in Scala (as in most +// other functional languages). // Recursive functions need an explicit return type, the compiler can't infer it. // Here it's Unit. def showNumbersInRange(a: Int, b: Int): Unit = { @@ -263,7 +274,7 @@ val x = 10 if (x == 1) println("yeah") if (x == 10) println("yeah") if (x == 11) println("yeah") -if (x == 11) println ("yeah") else println("nay") +if (x == 11) println("yeah") else println("nay") println(if (x == 10) "yeah" else "nope") val text = if (x == 10) "yeah" else "nope" @@ -274,21 +285,21 @@ val text = if (x == 10) "yeah" else "nope" ///////////////////////////////////////////////// val a = Array(1, 2, 3, 5, 8, 13) -a(0) -a(3) +a(0) // Int = 1 +a(3) // Int = 5 a(21) // Throws an exception val m = Map("fork" -> "tenedor", "spoon" -> "cuchara", "knife" -> "cuchillo") -m("fork") -m("spoon") +m("fork") // java.lang.String = tenedor +m("spoon") // java.lang.String = cuchara m("bottle") // Throws an exception val safeM = m.withDefaultValue("no lo se") -safeM("bottle") +safeM("bottle") // java.lang.String = no lo se val s = Set(1, 3, 7) -s(0) -s(1) +s(0) // Boolean = false +s(1) // Boolean = true /* Look up the documentation of map here - * http://www.scala-lang.org/api/current/index.html#scala.collection.immutable.Map @@ -309,15 +320,22 @@ s(1) // Why have this? val divideInts = (x: Int, y: Int) => (x / y, x % y) -divideInts(10, 3) // The function divideInts gives you the result and the remainder +// The function divideInts gives you the result and the remainder +divideInts(10, 3) // (Int, Int) = (3,1) // To access the elements of a tuple, use _._n where n is the 1-based index of // the element -val d = divideInts(10, 3) +val d = divideInts(10, 3) // (Int, Int) = (3,1) + +d._1 // Int = 3 +d._2 // Int = 1 -d._1 +// Alternatively you can do multiple-variable assignment to tuple, which is more +// convenient and readable in many cases +val (div, mod) = divideInts(10, 3) -d._2 +div // Int = 3 +mod // Int = 1 ///////////////////////////////////////////////// @@ -449,6 +467,9 @@ def matchEverything(obj: Any): String = obj match { // You can nest patterns: case List(List((1, 2, "YAY"))) => "Got a list of list of tuple" + + // Match any case (default) if all previous haven't matched + case _ => "Got unknown object" } // In fact, you can pattern match any object with an "unapply" method. This @@ -562,8 +583,8 @@ sendGreetings("Jane") // => "Hello Jane, 100 blessings to you and yours!" // Implicit function parameters enable us to simulate type classes in other // functional languages. It is so often used that it gets its own shorthand. The // following two lines mean the same thing: -def foo[T](implicit c: C[T]) = ... -def foo[T : C] = ... +// def foo[T](implicit c: C[T]) = ... +// def foo[T : C] = ... // Another situation in which the compiler looks for an implicit is if you have @@ -601,6 +622,9 @@ import scala.collection.immutable.{List => ImmutableList} // Import all classes, except some. The following excludes Map and Set: import scala.collection.immutable.{Map => _, Set => _, _} +// Java classes can also be imported. Scala syntax can be used +import java.swing.{JFrame, JWindow} + // Your programs entry point is defined in an scala file using an object, with a // single method, main: object Application { |