Introduction to Scala and Environment Setup

Overview

Welcome to the Scala tutorial series! In this first unit, we'll help you get set up with everything you need to start programming in Scala. We'll cover:

1. Installing Scala
2. Setting up an IDE
3. Using the Scala REPL

Installing Scala

Prerequisites

Before installing Scala, ensure you have Java Development Kit (JDK) installed on your machine. Scala runs on the Java Virtual Machine (JVM), and having the JDK is essential.

Verify Java Installation

java -version

If Java is not installed, download and install it from the Oracle website or use your package manager.

Install Scala

Scala can be installed via several methods. Here, we'll use Scala Build Tool (sbt), which also sets up a build environment that can be handy later.

Using SDKMAN

SDKMAN is a tool for managing parallel versions of multiple Software Development Kits on most Unix-based systems. Here’s how to install Scala using SDKMAN:

1. Install SDKMAN:

   curl -s "https://get.sdkman.io" | bash
   source "$HOME/.sdkman/bin/sdkman-init.sh"

2. Install Scala:

   sdk install scala

3. Verify installation:

   scala -version

Alternative: Direct Download

You can also download Scala directly from the official Scala website.

Setting Up an IDE

An Integrated Development Environment (IDE) enhances productivity with features like syntax highlighting, project management, and debugging.

IntelliJ IDEA

1. Download and install IntelliJ IDEA from the JetBrains website.

2. Open IntelliJ IDEA and select New Project.

3. Choose Scala from the list of project types. If the Scala plugin is not installed, IntelliJ will prompt you to install it.

4. Configure the SDK. Ensure you select your JDK installation.

5. Complete the project setup. IntelliJ will create a new Scala project for you.

Visual Studio Code

1. Download and install Visual Studio Code from the official website.

2. Open Visual Studio Code and go to the Extensions view by clicking on the Extensions icon in the Sidebar.

3. Search for the Metals extension (Scala language server) and install it.

4. Create a new Scala project by opening your terminal in VS Code and running:

   sbt new scala/hello-world.g8

Using the Scala REPL

The Scala REPL (Read-Eval-Print Loop) allows you to interactively run Scala code snippets, making it a great tool for learning and prototyping.

Starting the Scala REPL

Once Scala is installed, you can start the REPL by simply typing:

scala

Example Usage

Here are some basic commands to get you started:

• Define a variable:

  val x = 10

• Print something to the console:

  println("Hello, Scala!")

• Define a function:

  def add(a: Int, b: Int): Int = a + b

• Call the function:

  add(5, 7)

Exit the REPL by typing :quit or pressing Ctrl+D.

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Now that your environment is set up, you're ready to start coding in Scala! Continue to the next unit for more in-depth programming tutorials and advanced topics.

Installing Scala and Necessary Tools

In this section, we will cover the installation of Scala and the tools required to start developing in Scala, set up an Integrated Development Environment (IDE), and use the Scala REPL (Read-Eval-Print Loop).

1. Installing Scala

To install Scala, you can use multiple methods. Here we will use “Scala installer” for simplicity.

Step 1: Install SDKMAN!

SDKMAN! is a tool for managing parallel versions of multiple Software Development Kits on most Unix-based systems.

# Install SDKMAN!
curl -s "https://get.sdkman.io" | bash
source "$HOME/.sdkman/bin/sdkman-init.sh"

Step 2: Install Scala

Once SDKMAN! is set up, you can install Scala by executing:

# Install the latest stable version of Scala
sdk install scala

Step 3: Verify Installation

Verify that Scala is installed successfully by checking its version:

scala -version

You should see output indicating the installed version of Scala.

2. Setting Up the IDE - IntelliJ IDEA

Step 1: Download and Install IntelliJ IDEA

Follow the Official JetBrains website to download and install Intellij IDEA.

Step 2: Install Scala Plugin

Once IntelliJ IDEA is installed, open it and perform the following to install the Scala plugin:

1. Navigate to File > Settings.
2. Select Plugins from the menu.
3. Search for Scala and click Install.
4. Restart IntelliJ IDEA to activate the plugin.

Step 3: Create a New Scala Project

1. Open IntelliJ IDEA and click on Create New Project.
2. Select Scala from the list of project types.
3. Make sure to select the appropriate JDK and click Next.
4. Name your project and select a location.
5. Click Finish to create the project.

3. Using the Scala REPL

Step 1: Launch the Scala REPL

Open your terminal and type:

scala

This command will start the Scala REPL, where you can execute Scala code interactively.

Step 2: Running Scala Code in REPL

Once in the Scala REPL, you can type Scala code to see immediate results. For example:

scala> println("Hello, Scala!")

You should see the output:

Hello, Scala!

Step 3: Exit the REPL

To exit the Scala REPL, simply type:

:quit

or press Ctrl+D.

Conclusion

You have successfully installed Scala, set up IntelliJ IDEA as your IDE, and learned to use the Scala REPL. With these tools in hand, you are ready to start your Scala development.

Setting Up IntelliJ IDEA for Scala Development

Step 1: Install IntelliJ IDEA

If IntelliJ IDEA is not already installed on your machine, download and install the Community or Ultimate edition from the official website.

Step 2: Install the Scala Plugin

1. Open IntelliJ IDEA.
2. Navigate to File -> Settings (Windows/Linux) or IntelliJ IDEA -> Preferences (macOS).
3. In the Settings or Preferences window, go to Plugins on the left panel.
4. Search for "Scala" in the search bar.
5. Click on the Install button next to the Scala plugin.
6. Restart IntelliJ IDEA once the plugin is installed.

Step 3: Create a New Scala Project

1. Open IntelliJ IDEA and select Create New Project.
2. In the New Project window, select Scala on the left panel.
3. Choose sbt (Scala Build Tool) in the right panel.
4. Specify the project SDK: Make sure you select a JDK that is installed on your machine. You might need to add a new JDK if none are detected.
5. Click Next.

Step 4: Configure Project Details

1. Enter the Project Name and choose the Project Location.
2. Select the sbt version and Scala version you wish to use.
3. Click on Finish.

Step 5: Verify Your Scala Setup

1. Once the project opens, wait for sbt to resolve dependencies and set up the project completely.

2. Create a new Scala object:

   • Right-click on src/main/scala in the Project Explorer.
   • Navigate to New -> Scala Class.
   • Choose Object and provide a name for your object, e.g., HelloWorld.

3. Implement a simple Scala program:

   object HelloWorld {
      def main(args: Array[String]): Unit = {
         println("Hello, World!")
      }
   }

4. Run the Scala Object:

   • Right-click on the HelloWorld object.
   • Select Run 'HelloWorld'.

Step 6: Using Scala REPL in IntelliJ IDEA

1. Open the Terminal within IntelliJ IDEA (View -> Tool Windows -> Terminal).
2. Start Scala REPL by typing scala and hitting Enter.

scala

Now you can execute Scala commands directly. For example:

scala> println("Hello, Scala REPL!")

Conclusion

You have now set up IntelliJ IDEA for Scala development, created a simple Scala project, and verified it by running a basic Scala object. Additionally, you have accessed and used the Scala REPL within the IDE to execute Scala commands interactively.

Configuring Visual Studio Code for Scala

This section guides you on how to configure Visual Studio Code for Scala development. It covers installing necessary extensions, configuring your project, and verifying the setup.

Step 1: Install Necessary Extensions

1. Launch Visual Studio Code.
2. Install the Metals Extension:
   • Go to the Extensions view by clicking on the Extensions icon in the Activity Bar on the side of the window or by pressing Ctrl+Shift+X.
   • Search for "Metals" and click the install button.
3. Install the Scala (Metals) Extension:
   • In the Extensions view, search for "Scala (Metals)".
   • Click install to add the Scala (Metals) Extension.

Step 2: Create a New Scala Project

1. Open Command Palette:
   • Press Ctrl+Shift+P to open the Command Palette.
2. Create New Project:
   • Inside Command Palette, type Metals: New Scala Project and select it.
   • Follow the prompts to specify the name and location of your new project.

Step 3: Configure Build Tool (sbt)

1. Open the project in VS Code.
2. Setup sbt:
   • Ensure you have an sbt build file named build.sbt at the root of your project:

     name := "my-scala-project"
     
     version := "0.1.0"
     
     scalaVersion := "2.13.6"
     
     libraryDependencies += "org.scalatest" %% "scalatest" % "3.2.9" % Test

Step 4: Verify Configuration

1. Ensure the Metals Server is Running:

   • When you open the project, Metals might prompt you to import the build. Click "Import Build" if prompted.

2. Compile the Project:

   • Open the Terminal in VS Code (`Ctrl+```) and run:

     sbt compile

3. Run the Scala REPL:

   • Open the Command Palette again (Ctrl+Shift+P).
   • Type Metals: Run Worksheet and select it.
   • Enter Scala code in the opened worksheet file (e.g., example.sc):

     println("Hello, Scala!")

4. Run Main Application:

   • Create a Scala file in src/main/scala:

     object Main extends App {
       println("Hello, World!")
     }

   • Run the application by pressing F5 or by running:

     sbt run

This setup allows you to develop, compile, and run Scala applications using Visual Studio Code. Ensure your project configurations and build tool settings are correctly set up for effective development.

Exploring the Scala REPL

The Scala REPL (Read-Eval-Print Loop) is an interactive shell that allows you to write and execute Scala code in real-time. It's a powerful tool for experimenting with code, testing functions, and understanding how Scala works. In this part, we will explore how to effectively use the Scala REPL.

Starting the Scala REPL

Once you have Scala installed, you can start the REPL by opening a terminal and executing:

scala

You should see the REPL prompt, which is typically represented by an arrow (scala>):

Welcome to Scala 2.13.3 (OpenJDK 64-Bit Server VM, Java 11.0.2). Type in expressions for evaluation. Or try :help.

scala>

Basic Commands

You can type Scala expressions directly into the REPL and see the results immediately. Here are some basic examples:

scala> 1 + 1
res0: Int = 2

scala> val x = 10
x: Int = 10

scala> x * 2
res1: Int = 20

In the above example:

• res0 and res1 are automatically named result variables.
• val x = 10 defines a new immutable variable x.

Defining Functions

You can define functions in the REPL to reuse code snippets:

scala> def add(a: Int, b: Int): Int = a + b
add: (a: Int, b: Int)Int

scala> add(3, 4)
res2: Int = 7

Working with Collections

Scala collections can also be used directly within the REPL:

scala> val numbers = List(1, 2, 3, 4, 5)
numbers: List[Int] = List(1, 2, 3, 4, 5)

scala> numbers.map(_ * 2)
res3: List[Int] = List(2, 4, 6, 8, 10)

Exploring Object-Oriented Features

You can define classes and objects to see OOP principles in action:

scala> class Person(val name: String, val age: Int)
defined class Person

scala> val alice = new Person("Alice", 25)
alice: Person = Person@1b6d3586

scala> alice.name
res4: String = Alice

scala> alice.age
res5: Int = 25

Using :help Command

You can use the :help command to see a list of special commands available in the REPL:

scala> :help
All commands can be abbreviated, e.g., :he instead of :help.
:load                   load and interpret a Scala file
:quit                         exit the interpreter
:reset                        reset the interpreter, forgetting all session entries
:sh             run a shell command (result is implicitly => List[String])
:help []            print the usage message for or describe 

Exiting the Scala REPL

To exit the REPL, you can use the :quit command:

scala> :quit

Or you can use the shortcut Ctrl + D (may vary depending on the terminal).

Conclusion

The Scala REPL is an essential tool for anyone learning Scala. It provides a quick feedback loop, making it perfect for experimenting with Scala syntax, testing functions and classes, and getting familiar with Scala's features. By mastering the REPL, you can significantly speed up your Scala learning process.

Creating and Running Your First Scala Program

Now that you've set up your Scala environment and IDE, it's time to create and run your first Scala program. We will walk you through writing a simple "Hello, World!" application in Scala.

Step 1: Create a New Scala Project

1. Open Your IDE: Open IntelliJ IDEA or Visual Studio Code where you have previously configured the Scala plugin.

2. Create a New Project:

   • IntelliJ IDEA:
     • Go to File > New > Project.
     • Select Scala from the project types, then proceed.
   • Visual Studio Code:
     • Create a new folder for your project, then open this folder in VS Code.

Step 2: Create a Scala Object

1. Create a New Scala File:

   • In your project folder, create a new directory named src (if it doesn't already exist).
   • Inside src, create a directory named main, and inside main, create another directory named scala.

2. Create a Scala File:

   • Inside src/main/scala, create a new file named HelloWorld.scala.

3. Write Your Scala Code:

   • Open HelloWorld.scala and add the following code:

object HelloWorld {
  def main(args: Array[String]): Unit = {
    println("Hello, World!")
  }
}

Step 3: Compile and Run Your Scala Program

1. Compile the Program:

   • Using IntelliJ IDEA:
     • Right-click on HelloWorld.scala in the project explorer and select Run 'HelloWorld'.
   • Using Visual Studio Code:
     • Open the terminal (Ctrl + `) and navigate to your project directory.
     • Run the following command to compile the program:

     scalac src/main/scala/HelloWorld.scala

2. Run the Compiled Code:

   • IntelliJ IDEA:

     • The IDE should automatically compile and run the program, showing "Hello, World!" in the console output.

   • Visual Studio Code:

     • Run the following command in the terminal:

     scala HelloWorld

     • You should see the output:

     Hello, World!

Congratulations! You have successfully created and run your first Scala program.

Best Practices for a Productive Scala Development Environment

Structuring Your Project

A well-structured project is crucial for maintaining code readability and manageability. In Scala, the typical structure follows the SBT (Simple Build Tool) convention:

my-scala-project/
|-- build.sbt
|-- project/
|-- src/
    |-- main/
    |   |-- scala/
    |   |   |-- com/
    |   |       |-- example/
    |   |           |-- Main.scala
    |-- test/
        |-- scala/
            |-- com/
                |-- example/
                    |-- MainSpec.scala

build.sbt Example

The build.sbt file defines your project's settings and dependencies. Here is a basic example:

name := "MyScalaProject"
version := "0.1"
scalaVersion := "2.13.6"

libraryDependencies ++= Seq(
  "org.scalatest" %% "scalatest" % "3.2.9" % Test
)

Code Formatting

Using a consistent code style is essential for collaborative programming. scalafmt is a popular tool for automatically formatting Scala code.

Install scalafmt by adding it to your project/plugins.sbt:

addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.4.6")

Configure scalafmt by creating a .scalafmt.conf file in the root of your project:

version = 2.4.6
maxColumn = 100
docstrings = ScalaDoc
includeCurlyBraceInSelectChains = false
align.preset = most

Run scalafmt via SBT:

sbt scalafmt

Using Linting Tools

Static code analysis tools help you find potential issues before they become bugs. Scalastyle and Scapegoat are two popular linting tools.

Add Scalastyle to your project/plugins.sbt:

addSbtPlugin("org.scalastyle" % "scalastyle-sbt-plugin" % "1.0.0")

Add Scapegoat to your build.sbt:

addSbtPlugin("com.sksamuel.scapegoat" % "sbt-scapegoat" % "1.3.11")
scapegoatVersion in ThisBuild := "1.3.11"

Running Linting Tools

Run Scalastyle using SBT:

sbt scalastyle

Run Scapegoat using SBT:

sbt scapegoat

Unit Testing

Testing is a fundamental part of any productive development environment. ScalaTest is the most commonly used testing library.

Here's an example of a unit test using ScalaTest:

// src/test/scala/com/example/MainSpec.scala
import org.scalatest.flatspec.AnyFlatSpec

class MainSpec extends AnyFlatSpec {

  "The Main object" should "say hello" in {
    assert(Main.hello() == "Hello, world!")
  }
}

Continuous Integration

Automate your build and testing process using a CI service like GitHub Actions. Create a .github/workflows/scala.yml file:

name: Scala CI

on:
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]

jobs:
  build:
    runs-on: ubuntu-latest

    steps:
    - uses: actions/checkout@v2

    - name: Set up JDK 11
      uses: actions/setup-java@v2
      with:
        java-version: '11'
        
    - name: Cache SBT
      uses: actions/cache@v2
      with:
        path: |
          ~/.ivy2/cache
          ~/.sbt
        key: ${{ runner.os }}-sbt-${{ hashFiles('**/build.sbt') }}
        restore-keys: |
          ${{ runner.os }}-sbt
        
    - name: sbt test
      run: sbt test

Conclusion

By following these best practices, you will ensure a productive and maintainable Scala development environment. These practices will help your team write clean, well-structured code, and catch issues early in the development lifecycle.