无涯教程-Scala - 模式匹配在函数值和闭包之后，模式匹配是Scala第二广泛使用的函数， Scala在处理消息时

在函数值和闭包之后，模式匹配是Scala第二广泛使用的函数， Scala在处理消息时为模式匹配提供了强大的支持。

Pattern - 示例

object Demo {
   def main(args: Array[String]) {
      println(matchTest(3))
   }
def matchTest(x: Int): String=x match {
case 1 => "one"
case 2 => "two"
case _ => "many"
}
}

将上述程序保存在 Demo.scala 中。以下命令用于编译和执行该程序。

\>scalac Demo.scala
\>scala Demo

many

带case语句的块定义一个函数，该函数将整数映射到字符串。 match关键字提供了将函数(如上面的模式匹配函数)应用于对象的便捷方法。

Pattern - 示例

object Demo {
   def main(args: Array[String]) {
      println(matchTest("two"))
      println(matchTest("test"))
      println(matchTest(1))
   }
def matchTest(x: Any): Any=x match {
case 1 => "one"
case "two" => 2
case y: Int => "scala.Int"
case _ => "many"
}
}

将上述程序保存在 Demo.scala 中。以下命令用于编译和执行该程序。

\>scalac Demo.scala
\>scala Demo

2
many
one

Case类进行匹配

case类是用于与case表达式进行模式匹配的特殊类，从语法上讲，这些是带有特殊修饰符的标准类: case 。

object Demo {
   def main(args: Array[String]) {
      val alice=new Person("Alice", 25)
      val bob=new Person("Bob", 32)
      val charlie=new Person("Charlie", 32)
  </span><span class="kwd">for</span><span class="pln"> </span><span class="pun">(</span><span class="pln">person </span><span class="pun">&lt;-</span><span class="pln"> </span><span class="typ">List</span><span class="pun">(</span><span class="pln">alice</span><span class="pun">,</span><span class="pln"> bob</span><span class="pun">,</span><span class="pln"> charlie</span><span class="pun">))</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
     person match </span><span class="pun">{</span><span class="pln">
        </span><span class="kwd">case</span><span class="pln"> </span><span class="typ">Person</span><span class="pun">(</span><span class="str">"Alice"</span><span class="pun">,</span><span class="pln"> </span><span class="lit">25</span><span class="pun">)</span><span class="pln"> </span><span class="pun">=&gt;</span><span class="pln"> println</span><span class="pun">(</span><span class="str">"Hi Alice!"</span><span class="pun">)</span><span class="pln">
        </span><span class="kwd">case</span><span class="pln"> </span><span class="typ">Person</span><span class="pun">(</span><span class="str">"Bob"</span><span class="pun">,</span><span class="pln"> </span><span class="lit">32</span><span class="pun">)</span><span class="pln"> </span><span class="pun">=&gt;</span><span class="pln"> println</span><span class="pun">(</span><span class="str">"Hi Bob!"</span><span class="pun">)</span><span class="pln">
        </span><span class="kwd">case</span><span class="pln"> </span><span class="typ">Person</span><span class="pun">(</span><span class="pln">name</span><span class="pun">,</span><span class="pln"> age</span><span class="pun">)</span><span class="pln"> </span><span class="pun">=&gt;</span><span class="pln"> println</span><span class="pun">(</span><span class="pln">
           </span><span class="str">"Age: "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> age </span><span class="pun">+</span><span class="pln"> </span><span class="str">" year, name: "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> name </span><span class="pun">+</span><span class="pln"> </span><span class="str">"?"</span><span class="pun">)</span><span class="pln">
     </span><span class="pun">}</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">

}
case class Person(name: String, age: Int)
}

将上述程序保存在 Demo.scala 中。以下命令用于编译和执行该程序。

\>scalac Demo.scala
\>scala Demo

Hi Alice!
Hi Bob!
Age: 32 year, name: Charlie?

首先，编译器自动将构造函数参数转换为不可变的字段(值)， val关键字是可选的，如果要使用可变字段，请使用var关键字。

其次，编译器自动为类实现 equals，hashCode，和 toString 方法，这些方法使用指定为构造函数参数的字段。因此，我们不需要自己的toString()方法。

最后， Person 类的主体也将变为空，因为不需要定义任何方法!

无涯教程-Scala - 模式匹配

Pattern - 示例

Pattern - 示例

Case类进行匹配

参考链接