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Changes for page WebObjects with Scala

Last modified by Ravi Mendis on 2011/05/10 02:10
From version 318.1
edited by Ravi Mendis
on 2010/01/20 01:23
Change comment: There is no comment for this version
To version 317.1
edited by Ravi Mendis
on 2011/05/10 02:06
Change comment: There is no comment for this version

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1 1  === What is Scala? ===
2 2  
3 -[[Scala>>http://en.wikipedia.org/wiki/Scala_(programming_language)]] is a language for concurrent computing.
4 -In this day and age of multi-core processors, concurrent computing can't be ignored.
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 Scala's features have been designed with concurrency in mind.
7 -Some of these may not be unfamiliar to Objective-C or WebObjects developers.
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:
8 8  
9 -Here's a quick summary:
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
10 10  
11 -|= |= Objective-C |= Java |= Scala
12 -|= Mutable/Immuable Datatypes | Collections //e.g: NSArray/NSMutableArray// | No | Yes
13 -|= Closures | Blocks (//Extension//) | No | Anonymous Functions
14 -|= Static variables | Yes | Yes | No
15 -|= Static methods or functions| Yes | Yes | No
16 -|= Concurrency | [[Grand Central Dispatch>>http://en.wikipedia.org/wiki/Grand_Central_Dispatch]] (//Extension//)| //Threads// |[[Actors>>http://en.wikipedia.org/wiki/Actor_model]]
17 -|= |= Weakly Typed |=--Strongly Typed--|= Strongly Typed
18 -
19 19  Other notable features include:
20 20  
21 -|= |= Objective-C |= Java |= Scala
22 -|= Parametered methods | Yes //e.g: addObject: to~:// | No | Yes //e.g: add(object= ,to=)//
23 -|= 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)]]
24 24  
25 25  === Why Use Scala? ===
26 26  
27 -Scala is inherently thread-safe.
28 -It has concurrency that is effectively built-in to the language.
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).
29 29  
30 -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).
31 -
32 32  === Can WebObjects be Programmed In Scala? ===
33 33  
34 34  Yes. It is very simple.
35 -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.
36 36  
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 +
37 37  = WebObjects In Scala =
38 38  
39 39  The following highlights some of the differences between Java and Scala in WebObjects:
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40 40  
41 41  == EOs in Scala ==
42 42  
43 -=== Thread-Safe Shared Vars ===
42 +=== Thread-Safe Shared Vars ===
44 44  
45 -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.
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.
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.
47 47  
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).
48 +
48 48  The following is an example of the use of a //Companion Object// for Talent in Scala instead of Talent static fields in Java.
49 49  
50 50  Java:
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51 51  
52 52  {{code value="java"}}
53 53  
54 -public class _Talent extends EOGenericRecord {
55 +public class Talent extends EOGenericRecord {
55 55   public static final String ENTITY_NAME = "Talent";
57 +}
56 56  
57 57  {{/code}}
58 58  
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60 60  
61 61  {{code}}
62 62  
63 -object Talent extends EOGenericRecord {
65 +object Talent {
64 64   val ENTITY_NAME = "Talent"
67 +}
65 65  
66 66  {{/code}}
67 67  
68 -==== Compacted imports ====
71 +This value will be accessed exactly the same way in both languages:
69 69  
70 -Two lines in Java are compacted into one in Scala.
73 +{{code}}
71 71  
75 +Talent.ENTITY_NAME
76 +
77 +{{/code}}
78 +
79 +==== Compacted imports ====
80 +
72 72  In Java:
73 73  
74 74  {{code value="java"}}
... ... @@ -153,13 +153,13 @@
153 153  
154 154  {{/code}}
155 155  
156 -==== Scala Annotations vs. Generic Accessors ====
165 +==== Scala Annotations vs. Generated Accessors ====
157 157  
158 -An example of accessing variables in WebObjects with the following languages:
167 +Here's an example of accessing variables in the following languages:
159 159  
160 -|= |= Objective-C |= Java |= Scala
161 -|= getter | ##object name## | ##object.name()## | ##object.name##
162 -|= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
169 +|= |= Objective-C |= Java |= Scala
170 +|= getter | ##object name## | ##object.name()## | ##object.name##
171 +|= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
163 163  
164 164  Of course in Java, we may generate WebObjects classes with "get" methods as well in order to stick to convention.
165 165  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.
... ... @@ -169,6 +169,8 @@
169 169  
170 170  {{code}}
171 171  
181 +import scala.reflect.BeanProperty
182 +
172 172  @BeanProperty var username = new String()
173 173  @BeanProperty var password = new String()
174 174  @BeanProperty var isAssistantCheckboxVisible = false
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177 177  
178 178  == How to Use Scala Collections with EOF ==
179 179  
180 -One of the benefits of Scala is its very powerful, concurrency-ready collection classes - primarily ##List##, ##Map##, ##Seq## and ##Set##.
181 -Employing these instead of ##NSArray## and ##NSDictionary## in WebObjects/EOF may be challenging.
191 +To use the Scala Collections API with an NSArray or NSDictionary you simply need to add an import:
182 182  
183 -But one may modify the EO templates to produce API such as:
193 +{{code value="java"}}
184 184  
185 -{{code}}
195 +import scala.collection.JavaConversions._
186 186  
187 -def movies: NSArray[EOGenericRecord] = {
188 - storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[EOGenericRecord]]
189 -}
190 -
191 -def moviesList: List[EOGenericRecord] = {
192 - movies.objects.toList
193 -}
194 -
195 195  {{/code}}
196 196  
197 -== How to Add Scala to a WO Project ==
199 +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.
198 198  
201 +== How to Add Scala to a WO Project (in Eclipse) ==
202 +
199 199  {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
200 200  
201 -{{note title="Note"}}
202 -
203 -This is for Eclipse/WOLips IDE
204 -
205 -{{/note}}
206 -
207 207  == WO Scala Example ==
208 208  
209 209  The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
210 210  All the EO logic and WO components are in Scala.
211 -Only the Application class is Java.
209 +Only the Application class remains Java.
212 212  
213 213  It is based on the D2W Movies example.
214 214  
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216 216  
217 217  === Setup ===
218 218  
219 -1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
220 -1. Install and start the OpenBase OBMovies database.
217 +1. [[Install the Scala eclipse IDE>>http://download.scala-ide.org/]]
221 221  1. Right-click on Application.java and run as a WOApplication (as usual).
222 222  
223 -==== EO Templates ====
220 +{{note}}
224 224  
222 +Application can be made into a Scala class as well, but then you will have to create a launcher in Eclipse manually.
223 +
224 +{{/note}}
225 +
226 +== EO Templates ==
227 +
225 225  When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
226 226  
227 -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//##
230 +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##
228 228  1. Change the File Names Extension to "scala"
229 229  1. In Destination Paths set the Superclass Package (e.g: base)
230 230  1. Uncheck Java under Options