Changes for page WebObjects with Scala

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1	1	=== What is Scala? ===
2	2
3		-Scala is a modern language not unlike Groovy.
4		-It is said to be more powerful (and faster) than Groovy or Ruby which has been the reason for its adoption at sites like Twitter.
	3	+[[Scala>>http://www.scala-lang.org/]] is a modern, multi-paradigm JVM language that is most often compared to [[Groovy>>http://en.wikipedia.org/wiki/Groovy_(programming_language)]], [[Clojure>>http://en.wikipedia.org/wiki/Clojure]] or [[Erlang>>http://en.wikipedia.org/wiki/Erlang_(programming_language)]]. Its [[functional language>>http://en.wikipedia.org/wiki/Functional_programming]] foundations and built-in [[Actors>>http://en.wikipedia.org/wiki/Actor_model]] library make it especially attractive for concurrent computing. (Scala is an abbreviation for "scalable" hinting at its design goals).
5	5
6		-Many of its features and paradigms favor multi-threading and concurrency. Some of these may not be unfamiliar to Objective-C and WebObjects developers. Here's a summary:
	5	+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:
7	7
8		-|= |= Objective-C |= Java |= Scala
9		-|= Mutable/Immuable Datatypes | Collections //e.g: NSArray/NSMutableArray// | No | //All datatypes//
10		-|= Closures | Blocks (//Extension//) | No | Yes
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
	7	+|= |= Objective-C |= Java |= Scala
	8	+|= Immutability | Partial - via collections //e.g: NSArray/NSMutableArray// | No | Yes
	9	+|= Closures | Yes - via Blocks (//Extension//) | No | Yes - via Anonymous Functions
	10	+|= Static variables | Yes | Yes | No
	11	+|= Static methods | Yes | Yes | No
	12	+|= Concurrency | Yes - via [[Grand Central Dispatch>>http://en.wikipedia.org/wiki/Grand_Central_Dispatch]] (//Extension//) | //Yes - via Threads// | Yes - via [[Actors>>http://en.wikipedia.org/wiki/Actor_model]]
	13	+|= |= Weakly Typed |= --Strongly Typed-- |= Strongly Typed
15	15
16	16	Other notable features include:
17	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
	17	+|= |= Objective-C |= Java |= Scala
	18	+|= Parametered methods | Yes //e.g: addObject: to~:// | No | Yes //e.g: add(object= ,to=)//
	19	+|= Class composition | Yes - via Categories | Yes - via Interfaces | Yes - via [[Traits>>http://en.wikipedia.org/wiki/Trait_(computer_science)]]
21	21
22		-A fuller description of Scala can be found [[here>>http://en.wikipedia.org/wiki/Scala_(programming_language)]].
23		-
24	24	=== Why Use Scala? ===
25	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.
	23	+For WebObjects developers, Scala offers itself as a powerful, safe and easy-to-use solution for [[concurrent computing>>Building Concurrent Applications with WebObjects and Scala]]. (In other words, Scala Actors can be used for problems that would have normally required threads).
28	28
29		-Scala offers concurrency that is (effectively) built-in to the language and is inherently thread-safe.
30		-Developing Ajax (i.e asynchronous communication) with WO may well require concurrent request handling and thread-safe code, for which Scala is a better choice than Java.
31		-
32		-In addition it may offer new solutions for concurrency in WebObjects.
33		-
34	34	=== Can WebObjects be Programmed In Scala? ===
35	35
36	36	Yes. It is very simple.
37		-Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
	28	+By virtue of being a JVM-language, Scala compiles to java bytecode.
38	38
	30	+Furthermore, being a multi-paradigm language grants Scala easy WebObjects-interoperability.
	31	+
	32	+===== Caveats =====
	33	+
	34	+Legacy tool support is often cited as a weak point. The [[Eclipse Scala plugin>>http://www.scala-ide.org]] has been found to be slow at times and sometimes buggy.
	35	+
39	39	= WebObjects In Scala =
40	40
41	41	The following highlights some of the differences between Java and Scala in WebObjects:
...	...	@@ -42,36 +42,46 @@
42	42
43	43	== EOs in Scala ==
44	44
45		-=== Thread-Safe Shared Vars ===
	42	+=== Thread-Safe Shared Vars ===
46	46
47		-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.
48		-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.
	44	+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.
49	49
50		-In Java:
	46	+You don't have to worry about synchronizing access to shared mutable fields in a concurrent application.
	47	+(This is not however true when for example you have a ##val## declared as a ##NSMutableArray##. You will still have to synchronize when adding to or removing from this mutable field).
51	51
52		-{{code}}
	49	+The following is an example of the use of a //Companion Object// for Talent in Scala instead of Talent static fields in Java.
53	53
54		-public class _Talent extends EOGenericRecord {
	51	+Java:
	52	+
	53	+{{code value="java"}}
	54	+
	55	+public class Talent extends EOGenericRecord {
55	55	public static final String ENTITY_NAME = "Talent";
56	56
57	57	{{/code}}
58	58
59		-In Scala:
	60	+Scala:
60	60
61	61	{{code}}
62	62
63		-object _Talent extends EOGenericRecord {
	64	+object Talent {
64	64	val ENTITY_NAME = "Talent"
65	65
66	66	{{/code}}
67	67
68		-==== Compacted imports ====
	69	+This value will be accessed exactly the same way in both languages:
69	69
70		-Two lines in Java is compacted into one in Scala.
	71	+{{code}}
71	71
	73	+Talent.ENTITY_NAME
	74	+
	75	+{{/code}}
	76	+
	77	+==== Compacted imports ====
	78	+
72	72	In Java:
73	73
74		-{{code}}
	81	+{{code value="java"}}
75	75
76	76	import com.webobjects.eocontrol.EOGenericRecord;
77	77	import com.webobjects.eocontrol.EORelationshipManipulation;
...	...	@@ -94,7 +94,7 @@
94	94
95	95	In Java:
96	96
97		-{{code}}
	104	+{{code value="java"}}
98	98
99	99	public class MenuHeader extends WOComponent {
100	100
...	...	@@ -115,11 +115,11 @@
115	115	==== Simplified Exception Handling ====
116	116
117	117	Scala doesn't force you to catch exceptions unlike in Java.
118		-In addition, the syntax employs Scala's very powerful pattern matching to handle different exceptions.
	125	+In addition, the syntax employs Scala's very powerful **pattern matching** to handle exceptions.
119	119
120	120	In Java:
121	121
122		-{{code}}
	129	+{{code value="java"}}
123	123
124	124	try {
125	125	EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
...	...	@@ -153,35 +153,79 @@
153	153
154	154	{{/code}}
155	155
156		-== How to Add Scala to a WO Project ==
	163	+==== Scala Annotations vs. Generated Accessors ====
157	157
158		-{{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
	165	+Here's an example of accessing variables in the following languages:
159	159
160		-{{note title="Note"}}
	167	+|= |= Objective-C |= Java |= Scala
	168	+|= getter | ##object name## | ##object.name()## | ##object.name##
	169	+|= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
161	161
162		-This is for Eclipse/WOLips IDE
	171	+Of course in Java, we may generate WebObjects classes with "get" methods as well in order to stick to convention.
	172	+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.
163	163
164		-{{/note}}
	174	+E.g, in Main.scala we annotate our component keys with ##@BeanProperty## to automatically create public "set" and "get" methods.
	175	+These variables can then be accessed via //KVC//.
165	165
	177	+{{code}}
	178	+
	179	+import scala.reflect.BeanProperty
	180	+
	181	+@BeanProperty var username = new String()
	182	+@BeanProperty var password = new String()
	183	+@BeanProperty var isAssistantCheckboxVisible = false
	184	+
	185	+{{/code}}
	186	+
	187	+== How to Use Scala Collections with EOF ==
	188	+
	189	+To use the Scala Collections API with an NSArray or NSDictionary you simply need to add an import:
	190	+
	191	+{{code value="java"}}
	192	+
	193	+import scala.collection.JavaConversions._
	194	+
	195	+{{/code}}
	196	+
	197	+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.
	198	+
	199	+== How to Add Scala to a WO Project (in Eclipse) ==
	200	+
	201	+{{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
	202	+
166	166	== WO Scala Example ==
167	167
168		-The following example is a mixed Java/Scala version of the WO Movies D2W app.
	205	+The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
169	169	All the EO logic and WO components are in Scala.
170		-Only the Application class is Java.
	207	+Only the Application class remains Java.
171	171
	209	+It is based on the D2W Movies example.
	210	+
172	172	{{attachments patterns=".*zip"}}{{/attachments}}
173	173
174	174	=== Setup ===
175	175
176		-1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
177		-1. Install and run the OpenBase OBMovies database.
	215	+1. [[Install the Scala eclipse IDE>>http://www.scala-ide.org/]]
178	178	1. Right-click on Application.java and run as a WOApplication (as usual).
179	179
180		-==== EO Templates ====
	218	+{{note}}
181	181
182		-See: [[Scala templates>>http://wiki.objectstyle.org/confluence/display/WOL/EOGenerator+Templates+and+Additions]]
	220	+Application can be made into a Scala class as well, but then you will have to create a launcher in Eclipse manually.
183	183
	222	+{{/note}}
	223	+
	224	+== EO Templates ==
	225	+
184	184	When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
185	185
	228	+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##
186	186	1. Change the File Names Extension to "scala"
	230	+1. In Destination Paths set the Superclass Package (e.g: base)
187	187	1. Uncheck Java under Options
	232	+
	233	+== How to Build & Deploy a WebObjects Scala Project with Ant ==
	234	+
	235	+1. [[Download>>http://www.scala-lang.org/downloads]] and install Scala
	236	+1. Set ##scala.home## (the location Scala has been installed onto) in the project ##build.properties## file
	237	+1. [[Add the scalac task and properties>>Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
	238	+1. Run from the project directory: ##sudo ant clean install##