scala> val someNumbers = List(-11, -10, -5, 0, 5, 10)
someNumbers: List[Int] = List(-11, -10, -5, 0, 5, 10)
scala> someNumbers.filter((x: Int) => x > 0)
res1: List[Int] = List(5, 10)
// 等效于下面的占位符语法
scala> someNumbers.filter(_ > 0)
res2: List[Int] = List(5, 10)
// 另一个占位符例子
scala> val f = (_: Int) + (_: Int)
f: (Int, Int) => Int = <function2>
scala> f(5, 10)
res3: Int = 15
scala> var sum = 0
sum: Int = 0
scala> someNumbers.foreach(sum += _)
scala> sum
res10: Int = -11
一个函数,或者函数的一部分,可以赋值给一个变量:
// 下面的三种写法等效
scala> someNumbers.foreach(println _)
scala> someNumbers.foreach(x => println(x))
scala> someNumbers.foreach(println)
scala> def sum(a: Int, b: Int, c: Int) = a + b + c
sum: (a: Int, b: Int, c: Int)Int
scala> val a = sum _
a: (Int, Int, Int) => Int = <function3>
scala> a(1, 2, 3)
res7: Int = 6
scala> val b = sum(1, _: Int, 3)
b: Int => Int = <function1>
scala> b(2)
res8: Int = 6
参考:
- https://www.cnblogs.com/joymufeng/p/6866999.html
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