scala extractor (Extractor)

Extractor (Extractor)
We have previously used the scala very powerful pattern matching capabilities, and by pattern matching, we can quickly match the sample class member variables.
E.g:

// 1. 创建两个样例类
case class Person(name:String, age:Int)
case class Order(id:String)

def main(args: Array[String]): Unit = {
    // 2. 创建样例类对象，并赋值为Any类型
    val zhangsan:Any = Person("张三", 20)
    val order1:Any = Order("001")

    // 3. 使用match...case表达式来进行模式匹配
    // 获取样例类中成员变量
    order1 match {
        case Person(name, age) => println(s"姓名：${name} 年龄：${age}")
        case Order(id1) => println(s"ID为：${id1}")
        case _ => println("未匹配")
    }
}

That is not all classes can be such a pattern matching it? The answer is:
no. To support pattern matching, it must implement a extractor.

Define extractor
before we learned, and apply the method to achieve companion object class, you can use the class name to quickly build an object. Companion object, there is a unapply method. And apply contrast, unapply the object class for the dismantling of one element


to implement a class of the extractor, need only to implement a method in unapply associated objects of this class.
Syntax:
def unapply(stu:Student):Option[(类型1, 类型2, 类型3...)] = { if(stu != null) { Some((变量1, 变量2, 变量3...)) } else { None } }
Example
example illustrates
create a Student class that contains the name, age two fields
to achieve a class destructor, and expression pattern matching using the match to extract class field.
Reference Code:

class Student(var name:String, var age:Int)

object Student {
    def apply(name:String, age:Int) = {
        new Student(name, age)
    }

    def unapply(student:Student) = {
        val tuple = (student.name, student.age)

        Some(tuple)
    }
}

def main(args: Array[String]): Unit = {
    val zhangsan = Student("张三", 20)

    zhangsan match {
        case Student(name, age) => println(s"${name} => ${age}")
    }
}

result: