Changes for page WebObjects with Scala

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Author

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1		-XWiki.johnthuss
	1	+XWiki.rmendis

Content

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1	1	=== What is Scala? ===
2	2
3		-[[Scala>>http://en.wikipedia.org/wiki/Scala_(programming_language)]] is a JVM language that is a hybrid of Object-Oriented and Functional styles.  It is useful as complete general purpose replacement for Java.  But its built-in Actors library makes it especially attractive for concurrent computing.
	3	+[[Scala>>http://en.wikipedia.org/wiki/Scala_(programming_language)]] is a language for concurrent computing.
4	4	In this day and age of multi-core processors, concurrent computing can't be ignored.
5	5
6		-Many of Scala's features have been designed with concurrency in mind, primarily a preference for immutability and the use of other functional language paradigms.
	6	+Many of Scala's features have been designed with concurrency in mind.
7	7	Some of these may not be unfamiliar to Objective-C or WebObjects developers.
8	8
9	9	Here's a quick summary:
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24	24
25	25	=== Why Use Scala? ===
26	26
27		-Scala can help you to write thread-safe code.
28		-It has concurrency that is built-in to the standard library, primarily via Actors.
	27	+Scala is inherently thread-safe.
	28	+It has concurrency that is effectively built-in to the language.
29	29
30	30	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).
31	31
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42	42
43	43	=== Thread-Safe Shared Vars ===
44	44
45		-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. Is this true?  I don't think Scala "object" instances (with the object keyword) are guaranteed to be thread-safe; they are just singletons
	45	+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.
46	46
47	47	So you don't have to worry about synchronizing access to shared mutable fields in a concurrent application.
48	48
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188	188
189	189	== How to Use Scala Collections with EOF ==
190	190
191		-To use the Scala Collections API with an NSArray or NSDictionary you simply need to add an import:import scala.collection.JavaConversions.
	191	+One of the benefits of Scala is its very powerful, concurrency-ready collection classes - primarily ##List##, ##Map## and ##Set##.
	192	+Employing these instead of ##NSArray## and ##NSDictionary## in WebObjects/EOF may be challenging.
192	192
193		-Then you can 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.  Alternatively, you could generate an actual new scala.List instance by calling myNSArray.toList.
	194	+But one may modify the EO templates to produce API such as:
194	194
	196	+{{code}}
	197	+
	198	+import scala.collection.JavaConversions._
	199	+
	200	+def movies = {
	201	+ storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[Movie]]
	202	+}
	203	+
	204	+def moviesList = {
	205	+ movies.asInstanceOf[java.lang.Iterable[Movie]].toList
	206	+}
	207	+
	208	+{{/code}}
	209	+
	210	+This employs a feature of Scala known as **implicit conversions** to automagically convert a NSArray (a Java Iterable) into a Scala Iterable.
	211	+
195	195	== How to Add Scala to a WO Project ==
196	196
197	197	{{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
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217	217	1. [[Install the Scala eclipse IDE>>http://www.scala-ide.org/]]
218	218	1. Right-click on Application.java and run as a WOApplication (as usual).
219	219
220		-Application can be made into a Scala class as well, but then you will have to create a launcher in Eclipse manually.
221		-
222	222	== EO Templates ==
223	223
224	224	When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor: