在迁移到 Scala 时与 Java 形成的习惯作斗争

One obvious one is to not take advantage of the nested scoping that scala allows, plus the delaying of side-effects (or realising that everything in scala is an expression):

public InputStream foo(int i) {
   final String s = String.valueOf(i);
   boolean b = s.length() > 3;
   File dir;
   if (b) {
       dir = new File("C:/tmp");
   } else {
       dir = new File("/tmp");
   }
   if (!dir.exists()) dir.mkdirs();
   return new FileInputStream(new File(dir, "hello.txt"));
}

可以转换为:

def foo(i : Int) : InputStream = {
   val s = i.toString
   val b = s.length > 3
   val dir = 
     if (b) {
       new File("C:/tmp")
     } else {
       new File("/tmp")
     }
   if (!dir.exists) dir.mkdirs()
   new FileInputStream(new File(dir, "hello.txt"))
}

但这可以改进很多.可能是:

def foo(i : Int) = {
   def dir = {
     def ensuring(d : File) = { if (!d.exists) require(d.mkdirs); d }
     def b = { 
       def s = i.toString
       s.length > 3
     }
     ensuring(new File(if (b) "C:/tmp" else "/tmp"));
   }
   new FileInputStream(dir, "hello.txt")
}