Scala for the Impatient

Scala Basics

Know the story behind Scala

Why Scala?

• Multi-paradigm language.
• Object-oriented and functional.
• Statically typed.
• Scalable from simple scripts to sophisticated (but still easy-to-use) libraries.
• Invented by Martin Odersky at EPFL.
• Works with Java VM tools/libraries/infrastructure.
• Used for big-iron projects in industry.
• Pragmatic choice as successor to Java (whose evolution has slowed to a crawl).
• Expands your mind and makes you think differently about programming in any language.

Scala Levels of Expertise

These lessons are A1 unless noted otherwise.

Use Scala worksheets

Live demo of worksheets

Work with values, variables, and fundamental data types

Declaring Variables

• Types Int, Double, Boolean, String.
• Arithmetic operators + - * / % like in Java.
• Variable type is inferred:

  val answer = 8 * 5 + 2 // answer is an Int

• Can specify type after the name:

  var greeting: String = null

• val: immutable, var: mutable.
  • Use val whenever you can.
• Semicolons at the end of a statement are optional.

Commonly Used Types

• Int, Double, Byte, Char, Short, Long, Float, Boolean.
• Everything is an object:

  1.to(10) // Apply to method to 1, returns Range(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

• The to method is actually defined in RichInt.
• java.lang.String is available in Scala.
• Augmented by > 100 methods in StringOps:

  "Hello".intersect("World") // Yields "lo"
  

• Big numbers are actually usable:

  val x: BigInt = 1234567890
  x * x * x // Yields 1881676371789154860897069000

• Infix notation:

  1 to 10 // Same as 1.to(10)
  1 + 10 // Same as 1.+(10)

• The ++, -- operators do not exist in Scala.
  • Use += instead: counter += 1.

Invoke functions and methods

Calling Functions and Methods

• Scala has both functions and methods:

  import scala.math._
  sqrt(2) // A function
  BigInt.probablePrime(100, scala.util.Random) // A method
  

• Methods without parameters usually don't use ():

  "Hello".distinct
  

  Rule of thumb: () only required for mutators
• Common to use (arg) for methods that are similar to function calls:

  "Hello"(4) // Yields 'o'

• Provided by apply method:

  "Hello".apply(4) // same as "Hello"(4)

Work with Scaladoc

Scaladoc

• Permalink: http://www.scala-lang.org/api/current
• Use the filter.
• Look inside companion objects (O = Object, C = Class).
• Look at packages (scala.math), RichXxx, StringOps.
• Methods can have function parameters:

  def count(p: (Char) => Boolean): Int

• Lots of classes. Use your intuition. Range, Seq[Char] mean what you think they do.
• Lots of methods.
• Don't freak out when you see the occasional indecipherable incantation:

  def scan[B >: Char, That](z: B)(op: (B, B) ⇒ B)(implicit cbf:
    CanBuildFrom[String, B, That]): That 

Practice using the worksheet, invoking functions, and reading Scaladoc

Lab

Part 1: The Scala Worksheet

1. Start the Scala IDE and make a new Scala project: File → New → Scala Project.
   Give a name Lesson1.
   Right-click on the project in the Package Explorer, then select New → Scala Worksheet. Call it Sheet1.
   Select Project from the menu and uncheck the Build Automatically checkbox.
   Make a new line before the } . Type 6 * 7 and then save (Ctrl+S/⌘+S). What do you get?
2. Edit the line to read val a = 6 * 7 and save. What do you get?
3. Add a. What do you get?
4. Add a = 43. What do you get? Why?
5. Remove that line and add val b; (This time with a semicolon.) What do you get? Why?
6. Change the line to val b: BigInt = 6 * 7. What do you get?
7. Add b.pow(1000). What do you get?

Part 2: Functions

1. Type import scala.math._ just above the }.
2. Below the import statement, type:

   sqrt(10)
   

   What do you get?
3. Type 1.to(10). What do you get?
4. Type 1.to(10).map(sqrt(_)). What do you get?
5. Type 6.*(7). What do you get? Why?

Part 3: Scaladoc

1. Open Scaladoc: http://www.scala-lang.org/api/current.
   Click on Int, then click on the large C icon. Watch it turn into an O.
   What is the Scala analog of java.lang.Integer.MAX_VALUE?
2. Type Str into the search box (next to the magnifying class Icon).
   Click on StringOps.
   Read the description of distinct.
   What do you expect the result of "Mississippi".distinct to be?
3. Try it out in the worksheet. Is that what you got?
4. Read the description of permutations.
   What do you expect the result of "Rhine".permutations to be?
5. That's not so good. Add .toArray. Now what do you get?
6. What do you get for "ABC".sum? Why? (Hint: Try 'A'.toInt and "ABC".sum.toInt)