1. The use of _* in scala
Scala allows the last parameter of a function to be repeated. This allows users to pass variable-length parameter lists to functions. To declare a repeating parameter, put an asterisk after the parameter's type.
1. Calculate the sum of 1 to 4
def main(args: Array[String]): Unit = {
val total = sum(1,2,3,4)
println(total)
}
def sum(args: Int*) = {
var result = 0
for (arg <- args) result += arg
result
}2. Use:_*
def main(args: Array[String]): Unit = {
val total = sum(1 to 5)
println(total)
}
def sum(args: Int*) = {
var result = 0
for (arg <- args) result += arg
result
}
报错是：
Error:(4, 26) type mismatch;
found : scala.collection.immutable.Range.Inclusive
required: Int
val total = sum(1 to 5)To achieve this function, you need to add a colon and a _* symbol after the array parameter. This way of writing tells the compiler to treat each element of arr as a parameter instead of passing it to the method as a single parameter. In the above code, you can use :_*
def main(args: Array[String]): Unit = {
val total = sum(1 to 4:_*)
println(total)
}
//变长参数
def sum(args: Int*) = {
var result = 0
for (arg <- args) result += arg
result
}3. :_* as a whole
:_* Taken as a whole, tell the compiler that you want a parameter to be treated as a sequence of parameters! For example, val s = sum(1 to 4:_*) treats 1 to 5 as a sequence of parameters.
https://shuqi.blog.csdn.net/article/details/113245405
Why does Scala's toSeq convert an immutable Set to a mutable ArrayBuffer? |
2. Operations in Scala:: , +:, :+, :::, +++, etc.
Beginners in Scala will definitely have some doubts about these operations: :: , +:, :+, :::, +++. Let’s summarize them today for your convenience.
/**
* scala中的:: , +:, :+, :::, +++, 等操作;
*/
object listTest {
def main(args: Array[String]): Unit = {
val list = List(1,2,3)
// :: 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
println(4 :: list) //输出: List(4, 1, 2, 3)
// .:: 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);
println( list.:: (5)) //输出: List(5, 1, 2, 3)
// :+ 用于在list尾部追加元素; list :+ x;
println(list :+ 6) //输出: List(1, 2, 3, 6)
// +: 用于在list的头部添加元素;
val list2 = "A"+:"B"+:Nil //Nil Nil是一个空的List,定义为List[Nothing]
println(list2) //输出: List(A, B)
// ::: 用于连接两个List类型的集合 list ::: list2
println(list ::: list2) //输出: List(1, 2, 3, A, B)
// ++ 用于连接两个集合，list ++ list2
println(list ++ list2) //输出: List(1, 2, 3, A, B)
}
}