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Wiki source code of WebObjects with Scala

Version 222.1 by Ravi Mendis on 2009/09/16 18:51
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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 === Accessors ===
67
68 In Scala:
69
70 {{code}}
71
72 def setFirstName(value: String) {
73 logger.debug( "updating firstName from " + firstName + " to " + value)
74 takeStoredValueForKey(value, _Talent.Keys.FIRST_NAME)
75 }
76
77 {{/code}}
78
79 === Compacted imports ===
80
81 Two lines in Java is compacted into one in Scala.
82
83 In Java:
84
85 {{code}}
86
87 import com.webobjects.eocontrol.EOGenericRecord;
88 import com.webobjects.eocontrol.EORelationshipManipulation;
89
90 {{/code}}
91
92 In Scala:
93
94 {{code}}
95
96 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
97
98 {{/code}}
99
100 == How to Program WebObjects In Scala ==
101
102 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
103
104 {{note title="Note"}}
105
106 This is for Eclipse/WOLips IDE
107
108 {{/note}}
109
110 == WO Scala Example ==
111
112 The following is a mixed Java/Scala version of the WO Movies D2W app.
113 All the EO logic and WO components are in Scala.
114 Only the Application class is Java.
115
116 {{attachments patterns=".*zip"}}{{/attachments}}
117
118 === Setup ===
119
120 1. Install and run the OpenBase OBMovies database.
121 1. Right-click on Application.java and run as a WOApplication (as usual).
122
123 ==== EO Templates ====
124
125 See: [[Scala templates>>http://wiki.objectstyle.org/confluence/display/WOL/EOGenerator+Templates+and+Additions]]
126
127 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
128
129 1. Change the File Names Extension to "scala"
130 1. Uncheck Java under Options