Changes for page WebObjects with Scala

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1	1	=== What is Scala? ===
	2	+
	3	+Scala is a modern language not unlike Groovy.
	4	+It is said to be more powerful (and faster) than Groovy or Rails which has been the reason for its adoption at sites like Twitter.
	5	+
	6	+Many of its features and paradigms favor multi-threaded and concurrent development which may not be unfamiliar to Objective-C and WebObjects developers. Here's a summary:
	7	+
	8	+|= |= Objective-C |= Java |= Scala
	9	+|= Mutable/Immuable Datatypes | Collections //e.g: NSArray/NSMutableArray// | No | //All datatypes//
	10	+|= Closures | Blocks (//Extension//) | No | //Built-in//
	11	+|= Static variables | Yes | Yes | No
	12	+|= Static methods/functions | Yes | Yes | No
	13	+|= Concurrency | [[Grand Central Dispatch>>http://en.wikipedia.org/wiki/Grand_Central_Dispatch]] (//Extension//)| //Threads// |[[Actors>>http://en.wikipedia.org/wiki/Actor_model]]
	14	+|= |= Weakly Typed |=--Strongly Typed--|= Strongly Typed
	15	+
	16	+Other notable features include:
	17	+
	18	+|= |= Objective-C |= Java |= Scala
	19	+|= Parametered methods | Yes //e.g: addObject: to~:// | No | Yes //e.g: add(object= ,to=)//
	20	+|= Class composition | Categories | Interfaces | Traits
	21	+
	22	+A fuller description of Scala can be found [[here>>http://en.wikipedia.org/wiki/Scala_(programming_language)]].
	23	+
	24	+=== Why Use Scala? ===
	25	+
	26	+With Web 2.0, building concurrent WebObjects applications is a must.
	27	+Developing and maintaining a concurrent or multi-threaded WebObjects application can be challenging.
	28	+
	29	+Scala offers concurrency that is (effectively) built-in to the language and is inherently thread-safe.
	30	+So it may offer new solutions for concurrency in WebObjects.
	31	+
	32	+=== Can WebObjects be Programmed In Scala? ===
	33	+
	34	+Yes. It is very simple.
	35	+Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
	36	+
	37	+= WebObjects In Scala =
	38	+
	39	+The following is an in-depth explanation of differences between Java and Scala in WebObjects:
	40	+
	41	+== EOs in Scala ==
	42	+
	43	+=== Thread-Safe Shared Constants and Vars ===
	44	+
	45	+Scala doesn't have static variables or methods. However, every class does have a //Companion Object// that will allow you to achieve something equivalent to static variables.
	46	+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.
	47	+
	48	+In Java:
	49	+
	50	+{{code}}
	51	+
	52	+public class _Talent extends EOGenericRecord {
	53	+ public static final String ENTITY_NAME = "Talent";
	54	+
	55	+{{/code}}
	56	+
	57	+In Scala:
	58	+
	59	+{{code}}
	60	+
	61	+object _Talent extends EOGenericRecord {
	62	+ val ENTITY_NAME = "Talent"
	63	+
	64	+{{/code}}
	65	+
	66	+==== Compacted imports ====
	67	+
	68	+Two lines in Java is compacted into one in Scala.
	69	+
	70	+In Java:
	71	+
	72	+{{code}}
	73	+
	74	+import com.webobjects.eocontrol.EOGenericRecord;
	75	+import com.webobjects.eocontrol.EORelationshipManipulation;
	76	+
	77	+{{/code}}
	78	+
	79	+In Scala:
	80	+
	81	+{{code}}
	82	+
	83	+import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
	84	+
	85	+{{/code}}
	86	+
	87	+== WOComponents in Scala ==
	88	+
	89	+==== Compact Constructors ====
	90	+
	91	+Scala allows for simpler use of multi-valued constructors than Java.
	92	+
	93	+In Java:
	94	+
	95	+{{code}}
	96	+
	97	+public class MenuHeader extends WOComponent {
	98	+
	99	+ public MenuHeader(WOContext aContext) {
	100	+ super(aContext);
	101	+ }
	102	+
	103	+{{/code}}
	104	+
	105	+In Scala:
	106	+
	107	+{{code}}
	108	+
	109	+class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
	110	+
	111	+{{/code}}
	112	+
	113	+==== Simplified Exception Handling ====
	114	+
	115	+Scala doesn't force you to catch exceptions unlike in Java.
	116	+In addition, the syntax employs Scala's very powerful pattern matching to handle different exceptions.
	117	+
	118	+In Java:
	119	+
	120	+{{code}}
	121	+
	122	+try {
	123	+ EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
	124	+ epi.setNextPage(context().page());
	125	+ nextPage = (WOComponent) epi;
	126	+} catch (IllegalArgumentException e) {
	127	+ ErrorPageInterface epf = D2W.factory().errorPage(session());
	128	+ epf.setMessage(e.toString());
	129	+ epf.setNextPage(context().page());
	130	+ nextPage = (WOComponent) epf;
	131	+}
	132	+
	133	+{{/code}}
	134	+
	135	+In Scala:
	136	+
	137	+{{code}}
	138	+
	139	+try {
	140	+ var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
	141	+ epi.setNextPage(context.page)
	142	+ nextPage = epi.asInstanceOf[WOComponent]
	143	+} catch {
	144	+ case e: IllegalArgumentException => {
	145	+ var epf: ErrorPageInterface = D2W.factory.errorPage(session)
	146	+ epf.setMessage(e.toString)
	147	+ epf.setNextPage(context.page)
	148	+ nextPage = epf.asInstanceOf[WOComponent]
	149	+ }
	150	+}
	151	+
	152	+{{/code}}
	153	+
	154	+== How to Add Scala to a WO Project ==
	155	+
	156	+{{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
	157	+
	158	+{{note title="Note"}}
	159	+
	160	+This is for Eclipse/WOLips IDE
	161	+
	162	+{{/note}}
	163	+
	164	+== WO Scala Example ==
	165	+
	166	+The following is a mixed Java/Scala version of the WO Movies D2W app.
	167	+All the EO logic and WO components are in Scala.
	168	+Only the Application class is Java.
	169	+
	170	+{{attachments patterns=".*zip"}}{{/attachments}}
	171	+
	172	+=== Setup ===
	173	+
	174	+1. Install and run the OpenBase OBMovies database.
	175	+1. Right-click on Application.java and run as a WOApplication (as usual).
	176	+
	177	+==== EO Templates ====
	178	+
	179	+See: [[Scala templates>>http://wiki.objectstyle.org/confluence/display/WOL/EOGenerator+Templates+and+Additions]]
	180	+
	181	+When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
	182	+
	183	+1. Change the File Names Extension to "scala"
	184	+1. Uncheck Java under Options