Trait Parameters番外編

Author: shinharad

step02/src/main/scala/com/github/shinharad/gettingStartedWithScala3/TraitParametersPart2.scala

@@ -0,0 +1,52 @@
+package com.github.shinharad.gettingStartedWithScala3
+package traitParametersPart2
+
+import scala.util.chaining.*
+
+//---
+// 番外編
+
+trait Greeting(val name: String):
+  def msg = s"How are you, $name"
+
+trait FormalGreeting extends Greeting:
+  override def msg = s"How do you do, $name"
+
+// コンパイルエラー
+// class A extends FormalGreeting
+
+class B extends Greeting("Bob"), FormalGreeting
+class C extends FormalGreeting, Greeting("Bob")
+
+// コンパイルエラー
+// trait FormalGreeting2(val name: String) extends Greeting:
+//   def msg = s"How do you do, $name"
+
+trait FormalGreeting3(override val name: String) extends Greeting:
+  override def msg = s"How do you do, $name"
+
+class D extends FormalGreeting3("Bill"), Greeting("Bob")
+class E extends Greeting("Bob"), FormalGreeting3("Bill")
+
+// コンパイルエラー
+// class F extends FormalGreeting3("Bill")
+// class G extends FormalGreeting3, Greeting("Bob")
+
+// コンパイルエラー
+// trait FormalGreeting4(override val name: String) extends Greeting(name):
+//   override def msg = s"How do you do, $name"
+
+@main def no1(): Unit =
+  println("-" * 50)
+
+  (new B).msg.tap(println)
+  (new C).msg.tap(println)
+  // => How do you do, Bob
+
+  println("-" * 10)
+
+  (new D).msg.tap(println)
+  (new E).msg.tap(println)
+  // => How do you do, Bill
+
+  println("-" * 50)