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| 1 | // ---------Framework:--------- | |
| 2 | ||
| 3 | abstract class Engine {
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| 4 | abstract type MixIn | |
| 5 | // add members to this base class which are defined only in the subclass | |
| 6 | class Base(val children: Seq[Base]) extends MixIn | |
| 7 | abstract def doSomething(base: Base) | |
| 8 | ||
| 9 | final class Spec1(val foo: String, children: Seq[Base]) extends Base(children) | |
| 10 | final class Spec2(val bar: String, children: Seq[Base]) extends Base(children) | |
| 11 | } | |
| 12 | ||
| 13 | object Engine {
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| 14 | def runExample(engine: Engine) {
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| 15 | val spec1 = new engine.Spec1("foo", Seq.empty)
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| 16 | engine.doSomething(spec1) | |
| 17 | val spec2 = new engine.Spec2("foo", Seq(new Spec1("foo", Seq.empty)))
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| 18 | engine.doSomething(spec2) | |
| 19 | } | |
| 20 | } | |
| 21 | ||
| 22 | // ---------Client:--------- | |
| 23 | ||
| 24 | class ConcreteEngine {
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| 25 | trait Height {
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| 26 | val height = if(children.isEmpty()) 0 else children.map{_.height}.max
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| 27 | } | |
| 28 | override type MixIn = Height | |
| 29 | ||
| 30 | override def doSomething(base: Base) {
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| 31 | println("Node @ " + base.height)
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| 32 | } | |
| 33 | } | |
| 34 | ||
| 35 | object Main extends App {
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| 36 | Engine.run(new ConcreteEngine()) | |
| 37 | } |
