What is Scala?

Scala is a language for concurrent computing.
In this day and age of multi-core processors, concurrent computing can't be ignored.

Many of Scala's features have been designed with concurrency in mind.
Some of these may not be unfamiliar to Objective-C or WebObjects developers.

Here's a quick summary:

	Objective-C	Java	Scala
Separation of Mutable & Immuable Datatypes	Collections e.g: NSArray/NSMutableArray	No	Yes
Closures	Blocks (Extension)	No	Anonymous Functions
Static variables	Yes	Yes	No
Static methods or functions	Yes	Yes	No
Concurrency	Grand Central Dispatch (Extension)	Threads	Actors
	Weakly Typed	Strongly Typed	Strongly Typed

Other notable features include:

Why Use Scala?

Scala is inherently thread-safe.
It has concurrency that is effectively built-in to the language.

So for WebObjects developers, Scala offers itself as a powerful, safe and easy-to-use solution for concurrent applications. (In other words, Scala Actors can be used for problems that would have normally required threads).

Can WebObjects be Programmed In Scala?

Yes. It is very simple.
Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.

WebObjects In Scala

The following highlights some of the differences between Java and Scala in WebObjects:

EOs in Scala

Thread-Safe Shared Vars

Scala doesn't have static variables or methods. However, a class can have a Companion Object that will allow you to achieve something equivalent to static variables.
One of the advantages of this approach is that it is thread-safe, so you don't have to worry about synchronizing access to these fields in a concurrent application.

The following is an example of the use of a Companion Object for Talent in Scala instead of Talent static fields in Java.

Java:

public class _Talent extends EOGenericRecord {
	public static final String ENTITY_NAME	= "Talent";

Scala:

object Talent extends EOGenericRecord {
	val ENTITY_NAME = "Talent"

Compacted imports

Two lines in Java are compacted into one in Scala.

In Java:

import com.webobjects.eocontrol.EOGenericRecord;
import com.webobjects.eocontrol.EORelationshipManipulation;

In Scala:

import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}

WOComponents in Scala

Compact Constructors

Scala allows for simpler use of multi-valued constructors than Java.

In Java:

public class MenuHeader extends WOComponent {

    public MenuHeader(WOContext aContext) {
        super(aContext);
    }

In Scala:

class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {

Simplified Exception Handling

Scala doesn't force you to catch exceptions unlike in Java.
In addition, the syntax employs Scala's very powerful pattern matching to handle exceptions.

In Java:

try {
    EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
    epi.setNextPage(context().page());
    nextPage = (WOComponent) epi;
} catch (IllegalArgumentException e) {
    ErrorPageInterface epf = D2W.factory().errorPage(session());
    epf.setMessage(e.toString());
    epf.setNextPage(context().page());
    nextPage = (WOComponent) epf;
}

In Scala:

try {
     var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
     epi.setNextPage(context.page)
     nextPage = epi.asInstanceOf[WOComponent]
} catch {
     case e: IllegalArgumentException => {
            var epf: ErrorPageInterface = D2W.factory.errorPage(session)
            epf.setMessage(e.toString)
            epf.setNextPage(context.page)
            nextPage = epf.asInstanceOf[WOComponent]
     }
}

Scala Annotations vs. Generated Accessors

An example of accessing variables in WebObjects with the following languages:

Of course in Java, we may generate WebObjects classes with "get" methods as well in order to stick to convention.
In scala there is an additional convenience we may use to produce "get" and "set" methods in addition to the default Scala accessors - Scala Annotations.

E.g, in Main.scala we annotate our component keys with @BeanProperty to automatically create public "set" and "get" methods.
These variables can then be accessed via KVC.

import scala.reflect.BeanProperty

@BeanProperty var username = new String()
@BeanProperty var password = new String()
@BeanProperty var isAssistantCheckboxVisible = false

How to Use Scala Collections with EOF

One of the benefits of Scala is its very powerful, concurrency-ready collection classes - primarily List, Map and Set.
Employing these instead of NSArray and NSDictionary in WebObjects/EOF may be challenging.

But one may modify the EO templates to produce API such as:

def movies: NSArray[Studio] = {
    storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[Studio]]
}
  
def moviesList: List[Studio] = {
    movies.objects.toList
}

How to Add Scala to a WO Project

1. Install the Scala eclipse IDE
2. Add Scala support to your WO project:
   1. Right-click your project in the WO Explorer
   2. In the context menu select Scala -> Add Scala Nature
3. Convert or use .scala instead of .java source

Note This is for Eclipse/WOLips IDE

WO Scala Example

The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
All the EO logic and WO components are in Scala.
Only the Application class is Java.

It is based on the D2W Movies example.

	Name	Size	Creator	Date	Comment
	WOScalaExample.zip	298 kb	Ravi Mendis	Jan 05, 2010	Proof of concept example v.5

Setup

1. Install the Scala eclipse IDE
2. Install and start the OpenBase OBMovies database.
3. Right-click on Application.java and run as a WOApplication (as usual).

EO Templates

When you create your .eogen file, be sure to make the following changes in the EOGenerator Editor:

1. Point to the local Scala versions of the .eotemplate files for Entity and _Entity
2. Change the File Names Extension to "scala"
3. In Destination Paths set the Superclass Package (e.g: base)
4. Uncheck Java under Options

How to Build & Deploy a WebObjects Scala Project with Ant

1. Download and install Scala
2. Set scala.home (the location Scala has been installed onto) in the project build.properties file
3. Add the scalac task and properties to the ant build.xml file
4. Run from the project directory: sudo ant clean install