Changes for page WebObjects with Scala

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

From version 508.1
edited by Ravi Mendis
on 2010/12/24 03:01
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To version 515.1
edited by Ravi Mendis
on 2009/09/30 18:01
Change comment: There is no comment for this version

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1 1  === What is Scala? ===
2 2  
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).
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.
4 4  
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:
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:
6 6  
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
8 +|= |= Objective-C |= Java |= Scala
9 +|= Mutable/Immuable Datatypes | Collections //e.g: NSArray/NSMutableArray// | No | Yes
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
14 14  
15 15  Other notable features include:
16 16  
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)]]
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
20 20  
22 +A fuller description of Scala can be found [[here>>http://en.wikipedia.org/wiki/Scala_(programming_language)]].
23 +
21 21  === Why Use Scala? ===
22 22  
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).
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.
24 24  
25 -=== Can WebObjects be Programmed In Scala? ===
29 +Scala offers concurrency that is (effectively) built-in to the language and is inherently thread-safe.
26 26  
27 -Yes. It is very simple.
28 -By virtue of being a JVM-language, Scala compiles to java bytecode.
31 +In other words, developing Ajax (i.e asynchronous communication) with WO will require concurrent request handling and thread-safe code, for which Scala is a better choice than Java.
29 29  
30 -Furthermore, being a multi-paradigm language grants Scala easy WebObjects-interoperability.
33 +In addition it may offer new solutions for concurrency in WebObjects and EOF.
31 31  
32 -===== Caveats =====
35 +=== Can WebObjects be Programmed In Scala? ===
33 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.
37 +Yes. It is very simple.
38 +Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
35 35  
36 36  = WebObjects In Scala =
37 37  
... ... @@ -39,46 +39,36 @@
39 39  
40 40  == EOs in Scala ==
41 41  
42 -=== Thread-Safe Shared Vars ===
46 +=== Thread-Safe Shared Vars ===
43 43  
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.
48 +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.
49 +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.
45 45  
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 +In Java:
48 48  
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 +{{code}}
50 50  
51 -Java:
52 -
53 -{{code value="java"}}
54 -
55 55  public class _Talent extends EOGenericRecord {
56 56   public static final String ENTITY_NAME = "Talent";
57 57  
58 58  {{/code}}
59 59  
60 -Scala:
60 +In Scala:
61 61  
62 62  {{code}}
63 63  
64 -object Talent {
64 +object _Talent extends EOGenericRecord {
65 65   val ENTITY_NAME = "Talent"
66 66  
67 67  {{/code}}
68 68  
69 -This value will be accessed exactly the same way in both languages:
70 -
71 -{{code}}
72 -
73 -Talent.ENTITY_NAME
74 -
75 -{{/code}}
76 -
77 77  ==== Compacted imports ====
78 78  
71 +Two lines in Java are compacted into one in Scala.
72 +
79 79  In Java:
80 80  
81 -{{code value="java"}}
75 +{{code}}
82 82  
83 83  import com.webobjects.eocontrol.EOGenericRecord;
84 84  import com.webobjects.eocontrol.EORelationshipManipulation;
... ... @@ -101,7 +101,7 @@
101 101  
102 102  In Java:
103 103  
104 -{{code value="java"}}
98 +{{code}}
105 105  
106 106  public class MenuHeader extends WOComponent {
107 107  
... ... @@ -122,11 +122,11 @@
122 122  ==== Simplified Exception Handling ====
123 123  
124 124  Scala doesn't force you to catch exceptions unlike in Java.
125 -In addition, the syntax employs Scala's very powerful **pattern matching** to handle exceptions.
119 +In addition, the syntax employs Scala's very powerful pattern matching to handle different exceptions.
126 126  
127 127  In Java:
128 128  
129 -{{code value="java"}}
123 +{{code}}
130 130  
131 131  try {
132 132   EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
... ... @@ -160,79 +160,35 @@
160 160  
161 161  {{/code}}
162 162  
163 -==== Scala Annotations vs. Generated Accessors ====
157 +== How to Add Scala to a WO Project ==
164 164  
165 -An example of accessing variables in WebObjects with the following languages:
159 +{{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
166 166  
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 +{{note title="Note"}}
170 170  
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 +This is for Eclipse/WOLips IDE
173 173  
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 +{{/note}}
176 176  
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 -
203 203  == WO Scala Example ==
204 204  
205 -The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
169 +The following example is a mixed Java/Scala version of the WO Movies D2W app.
206 206  All the EO logic and WO components are in Scala.
207 -Only the Application class remains Java.
171 +Only the Application class is Java.
208 208  
209 -It is based on the D2W Movies example.
210 -
211 211  {{attachments patterns=".*zip"}}{{/attachments}}
212 212  
213 213  === Setup ===
214 214  
215 -1. [[Install the Scala eclipse IDE>>http://www.scala-ide.org/]]
177 +1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
178 +1. Install and run the OpenBase OBMovies database.
216 216  1. Right-click on Application.java and run as a WOApplication (as usual).
217 217  
218 -{{note}}
181 +==== EO Templates ====
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.
183 +See: [[Scala templates>>http://wiki.objectstyle.org/confluence/display/WOL/EOGenerator+Templates+and+Additions]]
221 221  
222 -{{/note}}
223 -
224 -== EO Templates ==
225 -
226 226  When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
227 227  
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##
229 229  1. Change the File Names Extension to "scala"
230 -1. In Destination Paths set the Superclass Package (e.g: base)
231 231  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##