Question

尝试了解基本的Scala概念。为什么这段代码没有编译？

 case class User(
               id: Int,
               firstName: String,
               lastName: String,
               age: Int,
               gender: Option[String])

object UserRepository {
 val users = Map
 ( 1 ->  User(1, "John", "Doe", 32, Some("male")),
   2 -> User(2, "Johanna", "Doe", 30, None)
   )
//def findById(id: Int): Option[User] = users
//def findAll = users.values
def getUsers() = { users }
}

for ((k,v) <- UserRepository.getUsers() ){
 println(v)
}

错误：（25,42）值过滤器不是对象cala.collection.immutable.Map的成员 for（（k，v）＆lt; - UserRepository.getUsers（））{

我预计val用户正在持有Map？

简单地图工作正常：

val simpleMap = Map (1 -> "First", 2 -> "Second")

for ((k,v) <- simpleMap ){
 println(v)
}

Answer 1

   Route::post('posts', '....');

这是两个单独的表达式：首先执行val users = Map ( 1 -> User(1, "John", "Doe", 32, Some("male")), 2 -> User(2, "Johanna", "Doe", 30, None) )（在Scala中有效，并将类型为val users = Map的伴随对象分配给Map），然后评估

users

扔掉结果。如果您通过将( 1 -> User(1, "John", "Doe", 32, Some("male")), 2 -> User(2, "Johanna", "Doe", 30, None) )移到上面的行来告诉编译器定义尚未结束，那么它将起作用：

Answer 2

在Map之后立即启动括号，告诉scala编译器该括号属于Map

而不是这个

object UserRepository {
 val users = Map
 ( 1 ->  User(1, "John", "Doe", 32, Some("male")),
   2 -> User(2, "Johanna", "Doe", 30, None)
   )
//def findById(id: Int): Option[User] = users
//def findAll = users.values
def getUsers() = { users }
}

这样做

object UserRepository {
   val users = Map( 1 ->  User(1, "John", "Doe", 32, Some("male")),
     2 -> User(2, "Johanna", "Doe", 30, None)) //start parenthesis after Map
   //def findById(id: Int): Option[User] = users
   //def findAll = users.values
  def getUsers() = { users }
}

包含未按预期运行的对象的映射Scala

2 个答案: