Partial function of Scala

One 、 Definition

1. The quilt is wrapped in curly brackets match A group of case Statement is a partial function
2. The partial function is PartialFunction[A, B] An example of
  - A Represents the type of input parameter
  - B Represents the return result type
3. Partial functions are in scala Middle is a trait

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Two 、 example

1. demand

Give you a collection val list = List(1, 2, 3, "a", true) , Please complete the following requirements :
Set list Multiply all numbers in by 10, And return to a new set
It is required to ignore non numeric elements , That is, the new set form returned is (10,20,30)

2. Code

object _06PartialFunction {
  def main(args: Array[String]): Unit = {
    val list = List(1, 2, 3, "a", true)
    
    // The way 1
    list.filter(x => x.isInstanceOf[Int]).map(x => x.asInstanceOf[Int] * 10).foreach(println)
    println("-" * 60)
    
    // The way 2
    val list0 = list.collect{
      case x:Int => x * 10
    }
    list0.foreach(println)
    println("------list0------")
    
    // The way 3： Recommended use 
    val pf1:PartialFunction[Any, Int] = {
      case x:Int => x * 10
    }
    //collect Method , Be similar to map Method ,collect Methods can only pass partial functions 
    list.collect(pf1).foreach(println)
    println("------pf1------")
    
    // The way 4
    val pf2 = new PartialFunction[Any,Int] {
      // Return only true Give it to apply Handle 
      override def isDefinedAt(x: Any): Boolean = x.isInstanceOf[Int]
      // processing method 
      override def apply(v1: Any): Int = v1.asInstanceOf[Int] * 10
    }
    list.collect(pf2).foreach(println)
    println("------pf2------")
    
    // The way 5
    val pf3 = new PartialFunction[Any, Int] {
      override def isDefinedAt(x: Any): Boolean = x match {
        case a:Int => true
        case _ => false
      }
      override def apply(v1: Any): Int = v1 match {
        case a:Int => a * 10
      }
    }
    list.collect(pf3).foreach(println)
    println("------pf3------")

  }
}

Each of the above methods will print ：

10
20
30

3、 ... and 、 Summary of partial functions

1. Use implementation classes that build idiosyncrasies ( The way to use it is PartialFunction Anonymous subclass of );
2.PartialFunction It's a trait ( Look at the source code );
3. When constructing partial functions , Parameter form [Any, Int] Is a generic , The first represents the parameter type , The second represents the return parameter ;
4. When using partial functions , Will traverse all elements of the collection , The compiler executes the process first isDefinedAt() If true , Will execute apply, Building a new Int Object returns ;
5. perform isDefinedAt() by false Just filter out this element , That is, no new Int object ;
6.map Function does not support partial functions , because map The underlying mechanism is all loop traversal , Cannot filter elements of the original collection ;collect Functions support partial functions .