Scala:Tutorials about the Scala Programming Language

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关键词：Programming Tutorials Language Tutorial Program about

1. Scala code to read a text file to an Array (or Seq)
   
2. As a quick note, I use code like this read a text file into an Array, List, or Seq using Scala:
   
3. 
   
4. def readFile(filename: String): Seq[String] = {
   
5.     val bufferedSource = io.Source.fromFile(filename)
   
6.     val lines = (for (line <- bufferedSource.getLines()) yield line).toList
   
7.     bufferedSource.close
   
8.     lines
   
9. }

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1. How to shuffle (randomize) a list in Scala
   
2. As a quick note today, to shuffle a list in Scala, use this technique:
   
3. 
   
4. scala.util.Random.shuffle(List(1,2,3,4))

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1. How to use ScalaCheck in the SBT REPL (command line)
   
2. If you add ScalaCheck to an SBT project like this:
   
3. 
   
4. libraryDependencies += "org.scalacheck" %% "scalacheck" % "1.13.4" % "test"
   
5. it’s only available in the SBT “test” scope. This means that when you start a Scala REPL session inside of SBT with its console command, the ScalaCheck library won’t be available in that scope.
   
6. 
   
7. To use ScalaCheck with the SBT console (REPL), don’t use its console command — use test:console instead. A complete example looks like this:
   
8. 
   
9. $ sbt
   
10. 
    
11. > test:console
    
12. 
    
13. scala> import org.scalacheck.Gen.choose
    
14. Note that after you type test:console your project may be compiled, so that step may take a few moments.
    
15. 
    
16. In summary, use SBT’s console command to start a “normal” Scala REPL inside SBT, and use test:console to start a REPL that you can run tests inside of. (Note that this same advice also applies to using ScalaTest or

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1. Sealed classes are described in 'Programming in Scala', but sealed traits are not. Where can I find more information about a sealed trait?
   
2. 
   
3. I would like to know, if a sealed trait is the same as a sealed class? Or, if not, what are the differences? When is it a good idea to use a sealed trait (and when not)?
   
4. A sealed trait can be extended only in the same file as its declaration.
   
5. 
   
6. They are often used to provide an alternative to enums. Since they can be only extended in a single file, the compiler knows every possible subtypes and can reason about it.
   
7. 
   
8. For instance with the declaration:
   
9. 
   
10. sealed trait Answer
    
11. case object Yes extends Answer
    
12. case object No extends Answer
    
13. The compiler will emit a warning if a match is not exhaustive:
    
14. 
    
15. scala> val x: Answer = Yes
    
16. x: Answer = Yes
    
17. 
    
18. scala> x match {
    
19.      |   case No => println("No")
    
20.      | }
    
21. <console>:12: warning: match is not exhaustive!
    
22. missing combination            Yes
    
23. So you should use sealed traits (or sealed abstract class) if the number of possible subtypes is finite and known in advance. For more examples you can have a look at list and option implementations

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Thanks!!!!!!