diff options
Diffstat (limited to 'scala.html.markdown')
| -rw-r--r-- | scala.html.markdown | 77 |
1 files changed, 64 insertions, 13 deletions
diff --git a/scala.html.markdown b/scala.html.markdown index d33b6234..08fd37e4 100644 --- a/scala.html.markdown +++ b/scala.html.markdown @@ -25,7 +25,7 @@ Scala - the scalable language /* Try the REPL - Scala has a tool called the REPL (Read-Eval-Print Loop) that is anologus to + Scala has a tool called the REPL (Read-Eval-Print Loop) that is analogous to commandline interpreters in many other languages. You may type any Scala expression, and the result will be evaluated and printed. @@ -252,7 +252,7 @@ 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. -// It has no effect on anonymous functions. For example: +// It has no effect on anonymous functions. For example here you may expect foo(7) should return 17 but it returns 7: def foo(x: Int): Int = { val anonFunc: Int => Int = { z => if (z > 5) @@ -260,9 +260,10 @@ def foo(x: Int): Int = { else z + 2 // This line is the return value of anonFunc } - anonFunc(x) // This line is the return value of foo + anonFunc(x) + 10 // This line is the return value of foo } +foo(7) // => 7 ///////////////////////////////////////////////// // 3. Flow Control @@ -276,6 +277,8 @@ r foreach println // NB: Scala is quite lenient when it comes to dots and brackets - study the // rules separately. This helps write DSLs and APIs that read like English +// Why doesn't `println` need any parameters here? +// Stay tuned for first-class functions in the Functional Programming section below! (5 to 1 by -1) foreach (println) // A while loop @@ -299,7 +302,7 @@ do { // 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. +// Here it's Unit, which is analagous to a `void` return type in Java def showNumbersInRange(a: Int, b: Int): Unit = { print(a) if (a < b) @@ -343,7 +346,7 @@ 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 + * https://www.scala-lang.org/api/current/scala/collection/immutable/Map.html * and make sure you can read it */ @@ -412,8 +415,8 @@ class Dog(br: String) { private def sleep(hours: Int) = println(s"I'm sleeping for $hours hours") - // Abstract methods are simply methods with no body. If we uncomment the next - // line, class Dog would need to be declared abstract + // Abstract methods are simply methods with no body. If we uncomment the + // def line below, class Dog would need to be declared abstract like so: // abstract class Dog(...) { ... } // def chaseAfter(what: String): String } @@ -455,13 +458,57 @@ george.phoneNumber // => "1234" Person("George", "1234") == Person("Kate", "1236") // => false // Easy way to copy -// otherGeorge == Person("george", "9876") +// otherGeorge == Person("George", "9876") val otherGeorge = george.copy(phoneNumber = "9876") // And many others. Case classes also get pattern matching for free, see below. +// Traits +// Similar to Java interfaces, traits define an object type and method +// signatures. Scala allows partial implementation of those methods. +// Constructor parameters are not allowed. Traits can inherit from other +// traits or classes without parameters. + +trait Dog { + def breed: String + def color: String + def bark: Boolean = true + def bite: Boolean +} +class SaintBernard extends Dog { + val breed = "Saint Bernard" + val color = "brown" + def bite = false +} + +scala> b +res0: SaintBernard = SaintBernard@3e57cd70 +scala> b.breed +res1: String = Saint Bernard +scala> b.bark +res2: Boolean = true +scala> b.bite +res3: Boolean = false + +// A trait can also be used as Mixin. The class "extends" the first trait, +// but the keyword "with" can add additional traits. + +trait Bark { + def bark: String = "Woof" +} +trait Dog { + def breed: String + def color: String +} +class SaintBernard extends Dog with Bark { + val breed = "Saint Bernard" + val color = "brown" +} -// Traits coming soon! +scala> val b = new SaintBernard +b: SaintBernard = SaintBernard@7b69c6ba +scala> b.bark +res0: String = Woof ///////////////////////////////////////////////// @@ -479,7 +526,9 @@ def matchPerson(person: Person): String = person match { case Person(name, number) => "We matched someone : " + name + ", phone : " + number } -val email = "(.*)@(.*)".r // Define a regex for the next example. +// Regular expressions are also built in. +// Create a regex with the `r` method on a string: +val email = "(.*)@(.*)".r // 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 @@ -545,6 +594,8 @@ List("Dom", "Bob", "Natalia") foreach println // Combinators +// Using `s` from above: +// val s = Set(1, 3, 7) s.map(sq) @@ -564,8 +615,8 @@ List( ).filter(_.age > 25) // List(Person("Bob", 30)) -// Scala a foreach method defined on certain collections that takes a type -// returning Unit (a void method) +// Certain collections (such as List) in Scala have a `foreach` method, +// which takes as an argument a type returning Unit - that is, a void method val aListOfNumbers = List(1, 2, 3, 4, 10, 20, 100) aListOfNumbers foreach (x => println(x)) aListOfNumbers foreach println @@ -666,7 +717,7 @@ 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 +// Your programs entry point is defined in a scala file using an object, with a // single method, main: object Application { def main(args: Array[String]): Unit = { |