Scalaのマップ型

連想配列、ハッシュマップとか呼ばれるやつで、他の言語と同じくキーと値の組からなるコレクションのこと。

$  scala
Welcome to Scala version 2.10.3 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_51).
Type in expressions to have them evaluated.
Type :help for more information.

scala> val m = Map[String, Int]("Scala"->1, "Java"->2, "Ruby"->3)
m: scala.collection.immutable.Map[String,Int] = Map(Scala -> 1, Java -> 2, Ruby -> 3)

scala> m("Scala")
res0: Int = 1

scala> m("Clojure")
java.util.NoSuchElementException: key not found: Clojure
        at scala.collection.MapLike$class.default(MapLike.scala:228)
        at scala.collection.AbstractMap.default(Map.scala:58)
        at scala.collection.MapLike$class.apply(MapLike.scala:141)
        at scala.collection.AbstractMap.apply(Map.scala:58)
        at .<init>(<console>:9)
        at .<clinit>(<console>)
        at .<init>(<console>:7)
        at .<clinit>(<console>)
        at $print(<console>)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:606)
        at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:734)
        at scala.tools.nsc.interpreter.IMain$Request.loadAndRun(IMain.scala:983)
        at scala.tools.nsc.interpreter.IMain.loadAndRunReq$1(IMain.scala:573)
        at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:604)
        at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:568)
        at scala.tools.nsc.interpreter.ILoop.reallyInterpret$1(ILoop.scala:756)
        at scala.tools.nsc.interpreter.ILoop.interpretStartingWith(ILoop.scala:801)
        at scala.tools.nsc.interpreter.ILoop.command(ILoop.scala:713)
        at scala.tools.nsc.interpreter.ILoop.processLine$1(ILoop.scala:577)
        at scala.tools.nsc.interpreter.ILoop.innerLoop$1(ILoop.scala:584)
        at scala.tools.nsc.interpreter.ILoop.loop(ILoop.scala:587)
        at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply$mcZ$sp(ILoop.scala:878)
        at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:833)
        at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:833)
        at scala.tools.nsc.util.ScalaClassLoader$.savingContextLoader(ScalaClassLoader.scala:135)
        at scala.tools.nsc.interpreter.ILoop.process(ILoop.scala:833)
        at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:83)
        at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:96)
        at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:105)
        at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)


scala>