Changes for page WebObjects with Scala

Last modified by Ravi Mendis on 2011/05/10 02:10

From 531.1 to 532.1 From 533.1 to 534.1

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edited by Ravi Mendis
on 2010/08/10 05:51

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To version 533.1

edited by Ravi Mendis
on 2011/05/10 02:10

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@@ -1,39 +1,118 @@
  === What is Scala? ===
--[[Scala>>http://en.wikipedia.org/wiki/Scala_(programming_language)]] is a language for concurrent computing.
--In this day and age of multi-core processors, concurrent computing can't be ignored.
++[[Scala>>url:http://www.scala-lang.org/||shape="rect"]] is a modern, multi-paradigm JVM language that is most often compared to [[Groovy>>url:http://en.wikipedia.org/wiki/Groovy_(programming_language)||shape="rect"]], [[Clojure>>url:http://en.wikipedia.org/wiki/Clojure||shape="rect"]] and [[Erlang>>url:http://en.wikipedia.org/wiki/Erlang_(programming_language)||shape="rect"]]. Its [[functional language>>url:http://en.wikipedia.org/wiki/Functional_programming||shape="rect"]] foundations and built-in [[Actors>>url:http://en.wikipedia.org/wiki/Actor_model||shape="rect"]] library make it especially attractive for concurrent computing. (Scala is an abbreviation for "scalable" hinting at its design goals).
--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.
++In this day and age of multi-core processors concurrent computing can not be ignored. Many of the design features of Scala have been chosen with concurrency in mind, some of which may not be unfamiliar to Objective-C or WebObjects developers. Here's a summary:
--Here's a quick summary:
++|=(((
++
++)))|=(((
++Objective-C
++)))|=(((
++Java
++)))|=(((
++Scala
++)))
++|=(((
++Immutability
++)))|(((
++Partial - via collections //e.g: NSArray/NSMutableArray//
++)))|(((
++No
++)))|(((
++Yes
++)))
++|=(((
++Closures
++)))|(((
++Yes - via Blocks (//Extension//)
++)))|(((
++No
++)))|(((
++Yes - via Anonymous Functions
++)))
++|=(((
++Static variables
++)))|(((
++Yes
++)))|(((
++Yes
++)))|(((
++No
++)))
++|=(((
++Static methods
++)))|(((
++Yes
++)))|(((
++Yes
++)))|(((
++No
++)))
++|=(((
++Concurrency
++)))|(((
++Yes - via [[Grand Central Dispatch>>url:http://en.wikipedia.org/wiki/Grand_Central_Dispatch||shape="rect"]] (//Extension//)
++)))|(((
++//Yes - via Threads//
++)))|(((
++Yes - via [[Actors>>url:http://en.wikipedia.org/wiki/Actor_model||shape="rect"]]
++)))
++|=(((
++
++)))|=(((
++Weakly Typed
++)))|=(((
++(% style="text-decoration: line-through;" %)Strongly Typed
++)))|=(((
++Strongly Typed
++)))
--|= |= 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>>http://en.wikipedia.org/wiki/Grand_Central_Dispatch]] (//Extension//) | //Threads// | [[Actors>>http://en.wikipedia.org/wiki/Actor_model]]
--|= |= Weakly Typed |= --Strongly Typed-- |= Strongly Typed
--
  Other notable features include:
--|= |= Objective-C |= Java |= Scala
--|= Parametered methods | Yes //e.g: addObject: to~:// | No | Yes //e.g: add(object= ,to=)//
--|= Class composition | Categories | Interfaces | Traits
++|=(((
++
++)))|=(((
++Objective-C
++)))|=(((
++Java
++)))|=(((
++Scala
++)))
++|=(((
++Parametered methods
++)))|(((
++Yes //e.g: addObject: to~://
++)))|(((
++No
++)))|(((
++Yes //e.g: add(object= ,to=)//
++)))
++|=(((
++Class composition
++)))|(((
++Yes - via Categories
++)))|(((
++Yes - via Interfaces
++)))|(((
++Yes - via [[Traits>>url:http://en.wikipedia.org/wiki/Trait_(computer_science)||shape="rect"]]
++)))
  === Why Use Scala? ===
--Scala is inherently thread-safe.
--It has concurrency that is effectively built-in to the language.
++For WebObjects developers, Scala offers itself as a powerful, safe and easy-to-use solution for [[concurrent computing>>doc:Building Concurrent Applications with WebObjects and Scala]]. (In other words, Scala Actors can be used for problems that would have normally required threads).
--So for WebObjects developers, Scala offers itself as a powerful, safe and easy-to-use solution for [[concurrent applications>>Building Concurrent Applications with WebObjects and Scala]]. (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.
++ By virtue of being a JVM-language, Scala compiles to java bytecode.
++Furthermore, being a multi-paradigm language grants Scala easy WebObjects-interoperability.
++
++===== Caveats =====
++
++Legacy tool support is often cited as a weak point. The [[Eclipse Scala plugin>>url:http://www.scala-ide.org||shape="rect"]] has been found to be slow at times and sometimes buggy.
++
  = WebObjects In Scala =
  The following highlights some of the differences between Java and Scala in WebObjects:
@@ -42,18 +42,20 @@
  === Thread-Safe Shared Vars ===
--Scala doesn't have static variables or methods. Instead Scala employs the [[Singleton Pattern>>http://en.wikipedia.org/wiki/Singleton_pattern]] which is built into the language and is **thread-safe**: a class can have a //Companion Object// that will allow you to achieve something equivalent to static variables - but better.
++Scala doesn't have static variables or methods. Instead Scala employs the [[Singleton Pattern>>url:http://en.wikipedia.org/wiki/Singleton_pattern||shape="rect"]] which is built into the language and is **thread-safe**: a class can have a //Companion Object// that will allow you to achieve something equivalent to static variables - but better.
--So you don't have to worry about synchronizing access to shared mutable fields in a concurrent application.
++You don't have to worry about synchronizing access to shared mutable fields in a concurrent application.
++ (This is not however true when for example you have a {{code language="none"}}val{{/code}} declared as a {{code language="none"}}NSMutableArray{{/code}}. You will still have to synchronize when adding to or removing from this mutable field).
  The following is an example of the use of a //Companion Object// for Talent in Scala instead of Talent static fields in Java.
  Java:
--{{code value="java"}}
++{{code 0="java"}}
--public class _Talent extends EOGenericRecord {
++public class Talent extends EOGenericRecord {
  	public static final String ENTITY_NAME	= "Talent";
++}
  {{/code}}
@@ -61,8 +61,9 @@
  {{code}}
--object Talent extends EOGenericRecord {
++object Talent {
  	val ENTITY_NAME = "Talent"
++}
  {{/code}}
@@ -76,11 +76,9 @@
  ==== Compacted imports ====
--Two lines in Java are compacted into one in Scala.
--
  In Java:
--{{code value="java"}}
++{{code 0="java"}}
  import com.webobjects.eocontrol.EOGenericRecord;
  import com.webobjects.eocontrol.EORelationshipManipulation;
@@ -103,7 +103,7 @@
  In Java:
--{{code value="java"}}
++{{code 0="java"}}
  public class MenuHeader extends WOComponent {
@@ -110,6 +110,7 @@
      public MenuHeader(WOContext aContext) {
          super(aContext);
      }
++}
  {{/code}}
@@ -117,7 +117,7 @@
  {{code}}
--class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
++class MenuHeader(context: WOContext) extends WOComponent(context: WOContext)
  {{/code}}
@@ -124,11 +124,11 @@
  ==== 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 addition, the syntax employs Scala's very powerful **pattern matching** to handle exceptions.
  In Java:
--{{code value="java"}}
++{{code 0="java"}}
  try {
      EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
@@ -164,17 +164,41 @@
  ==== Scala Annotations vs. Generated Accessors ====
--An example of accessing variables in WebObjects with the following languages:
++Here's an example of accessing variables in the following languages:
--|= |= Objective-C |= Java |= Scala
--|= getter | ##object name## | ##object.name()## | ##object.name##
--|= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
++|=(((
++
++)))|=(((
++Objective-C
++)))|=(((
++Java
++)))|=(((
++Scala
++)))
++|=(((
++getter
++)))|(((
++{{code language="none"}}[WO:object name]{{/code}}
++)))|(((
++{{code language="none"}}object.name(){{/code}}
++)))|(((
++{{code language="none"}}object.name{{/code}}
++)))
++|=(((
++setter
++)))|(((
++{{code language="none"}}[object setName:aName]{{/code}}
++)))|(((
++{{code language="none"}}object.setName(aName){{/code}}
++)))|(((
++{{code language="none"}}object.name = aName{{/code}}
++)))
  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.
++ 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//.
++E.g, in Main.scala we annotate our component keys with {{code language="none"}}@BeanProperty{{/code}} to automatically create public "set" and "get" methods.
++ These variables can then be accessed via //KVC//.
  {{code}}
@@ -188,56 +188,44 @@
  == 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.
++To use the Scala Collections API with an NSArray or NSDictionary you simply need to add an import:
--But one may modify the EO templates to produce API such as:
++{{code 0="java"}}
--{{code}}
--
  import scala.collection.JavaConversions._
--def movies: NSArray[Movie] = {
--    storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[Movie]]
--}
--
--def moviesList: Iterable[Movie] = {
--    movies.asInstanceOf[java.lang.Iterable[Movie]]
--}
--
  {{/code}}
--== How to Add Scala to a WO Project ==
++After that, you may access the typical Scala collection methods directly on NSArray.  This employs a feature of Scala known as implicit conversions to automagically cast a NSArray (a Java Iterable) into a Scala Iterable while leaving the actual object unchanged.
--{{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
++== How to Add Scala to a WO Project (in Eclipse) ==
--{{note}}
++{{include 0="WOL:Adding Scala Support to a WOLips Project"/}}
--This is for Eclipse/WOLips IDE
--
--{{/note}}
--
  == 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.
++ All the EO logic and WO components are in Scala.
++ Only the Application class remains Java.
  It is based on the D2W Movies example.
--{{attachments patterns=".*zip"}}{{/attachments}}
++{{attachments patterns=".*zip"/}}
  === Setup ===
--1. [[Install the Scala eclipse IDE>>http://www.scala-ide.org/]]
--1. Install and start the OpenBase OBMovies database.
++1. [[Install the Scala eclipse IDE>>url:http://download.scala-ide.org/||shape="rect"]]
 . Right-click on Application.java and run as a WOApplication (as usual).
--==== EO Templates ====
++{{note}}
++Application can be made into a Scala class as well, but then you will have to create a launcher in Eclipse manually.
++{{/note}}
--When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
++== EO Templates ==
--1. Point to the local [[Scala versions>>http://wiki.objectstyle.org/confluence/display/WOL/EOGenerator+Templates+and+Additions]] of the .eotemplate files for ##Entity## and ##Entity##
++When you create your {{code language="none"}}.eogen{{/code}} file, be sure to make the following changes in the EOGenerator Editor:
++
++1. Point to the local [[Scala versions>>url:http://wiki.objectstyle.org/confluence/display/WOL/EOGenerator+Templates+and+Additions||shape="rect"]] of the .eotemplate files for {{code language="none"}}Entity{{/code}} and {{code language="none"}}_Entity{{/code}}
 . Change the File Names Extension to "scala"
 . In Destination Paths set the Superclass Package (e.g: base)
 . Uncheck Java under Options
@@ -244,15 +244,7 @@
  == How to Build & Deploy a WebObjects Scala Project with Ant ==
--1. [[Download>>http://www.scala-lang.org/downloads]] and install Scala
--1. Set ##scala.home## (the location Scala has been installed onto) in the project ##build.properties## file
--1. [[Add the scalac task and properties>>Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
--1. Run from the project directory: ##sudo ant clean install##
--
--== Caveats ==
--
--{{warning}}
--
--Currently mixed Scala and Java projects aren't supported by the Scala Eclipse IDE, though it is possible to do so providing your project is either mostly  Java or mostly Scala.
--
--{{/warning}}
++1. [[Download>>url:http://www.scala-lang.org/downloads||shape="rect"]] and install Scala
++1. Set {{code language="none"}}scala.home{{/code}} (the location Scala has been installed onto) in the project {{code language="none"}}build.properties{{/code}} file
++1. [[Add the scalac task and properties>>doc:Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
++1. Run from the project directory: {{code language="none"}}sudo ant clean install{{/code}}

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