scala :: /.::/ ::: / :+ / +: / ++ /

① :: 用于的是向队列的头部追加数据,产生新的列表, x::list,x就会添加到list的头部

    .:: 这个是list的一个方法;作用和上面的一样,把元素添加到头部位置; list.::(x)

② :::   用于连接两个 List 类型的集合

③ :+  用于在list尾部追加元素; list :+

④ +: 用于在list的头部添加元素

⑤ ++  用于连接两个集合，list1++list2

scala> val b:List[Int] = List(10,23,45)
b: List[Int] = List(10, 23, 45)

scala> b :: 1
<console>:26: error: value :: is not a member of Int
       b :: 1
         ^

scala> 1 :: b
res30: List[Int] = List(1, 10, 23, 45)

scala> b.::(2)
res31: List[Int] = List(2, 10, 23, 45)

scala> 2.::b
<console>:24: error: value :: is not a member of Int
       2.::b
         ^

scala> b:+6
res33: List[Int] = List(10, 23, 45, 6)

scala> 7+:b
res34: List[Int] = List(7, 10, 23, 45)

scala> val c:List[Int]=List(32,54)
c: List[Int] = List(32, 54)

scala> b ++ c
res35: List[Int] = List(10, 23, 45, 32, 54)

scala> val d:Array[String] = Array("A","B","C")
d: Array[String] = Array(A, B, C)

scala> d ++ b
res36: Array[Any] = Array(A, B, C, 10, 23, 45)

scala> d ::: b
<console>:28: error: type mismatch;
 found   : Array[String]
 required: List[?]
       d ::: b
         ^