对于Scala编程，我们收集了这些常见代码编写中的陷阱。这些技巧来自于DanielSobral，一个曾参加过FreeBSD项目和Java软件开发工程的Scala狂热爱好者。
  1、语法错误

  认为“yield”像”return”一样。有人会这样写：

for(i <- 0 to 10) {  
  if (i % 2 == 0)  
    yield i  
  else 
    yield -i  
} 

  正确的表示应该是：

for(i <- 0 to 10)   
yield {  
  if (i % 2 == 0)  
    i  
  else 
    -i  
} 

val xml=<root/> 

val xml.$equal$less(root).$slash$greater  

val xml = <root/> 

object MyScalaApp extends Application {    
  // ... body ...  
} 

val r = """(\d+)""".r  
val s = "--> 5 <---" 
s match {  
  case r(n) => println("This won't match")  
  case _ => println("This will")  
} 

val r = """(\d+)""".r  
val s = "--> 5 <---" 
r findFirstIn s match {  
  case Some(n) => println("Matches 5 to "+n)  
  case _ => println("Won't match")  
} 

val r = """.*(\d+).*""".r  
val s = "--> 5 <---" 
s match {  
  case r(n) => println("This will match the first group of r, "+n+", to 5")  
  case _ => println("Won't match")  
}

class User(val name: String, initialPassword: String) {  
  private lazy var encryptedPassword = encrypt(initialPassword, salt)  
  private lazy var salt = scala.util.Random.nextInt  

  private def encrypt(plainText: String, salt: Int): String = { ... }  
  private def decrypt(encryptedText: String, salt: Int): String = { ... }  

  def password = decrypt(encryptedPassword, salt)  
  def password_=(newPassword: String) = encrypt(newPassword, salt)  
} 

class User(initialName: String, initialPassword: String) {  
   private object fields {  
     var name: String = initialName;  
     var password: String = initialPassword;  
   }  
   def name = fields.name  
   def name_=(newName: String) = fields.name = newName  
   def password = fields.password  
   def password_=(newPassword: String) = fields.password = newPassword  
 } 

class User(name0: String, password0: String) {  
  private case class Fields(var name: String, var password0: String)  
  private object fields extends Fields(name0, password0)  


  def name = fields.name  
  def name_=(newName: String) = fields.name = newName  
  def password = fields.password  
  def password_=(newPassword: String) = fields.password = newPassword  
} 

case class Customer(name: String)  

class ValidatingCustomer(name0: String) extends Customer(name0) {  
  require(name0.length < 5)  

  def name_=(newName : String) =  
    if (newName.length < 5) error("too short")  
    else super.name_=(newName)  
}  

val cust = new ValidatingCustomer("xyz123") 

def checkList[A](l: List[A]) = l match {  
  case _ : List[Int] => println("List of Ints")  
  case _ : List[String] => println("List of Strings")  
  case _ => println("Something else")  
} 

def checkList[A](l: List[A])(implicit m: scala.reflect.Manifest[A]) = m.toString match {  
  case "int" => println("List of Ints")  
  case "java.lang.String" => println("List of Strings")  
  case _ => println("Something else")  
} 

implicit def string2Int(s: String): Int = s.toInt 

case class Age(n: Int)  
implicit def string2Age(s: String) = Age(s.toInt)  
implicit def int2Age(n: Int) = new Age(n)  
implicit def age2Int(a: Age) = a.n

case class Person(name: String)(implicit age: Int) 

  ◆使用这样的定义：

def equals(other: MyClass): Boolean 

override def equals(other: Any): Boolean  

ping `hostname`  

def matchingChars(string: String, characters: String) = {  
  var m = "" 
  for(i <- 0 until string.length)  
    if ((characters contains string(i)) && !(m contains string(i)))  
      m += string(i)  
  m  
} 

def matchingChars(string: String, characters: String) = {  
  var m = "" 
  for(c <- string)  
    if ((characters contains c) && !(m contains c))  
      m += c  
  m  
} 

def indicesOf(s: String, c: Char) = for {  
  (sc, index) <- s.zipWithIndex  
  if c == sc  
} yield index