定義「複製」方法的情況下類

Question

鑑於簡化代碼例如：

sealed trait A { 

    val c1: String 
    val c2: Int 

    def copy[Z <: A](src: File) : Z 

} 

case class B(c1: String, c2: Int, src: File) extends A 

case class C(c1: String, c2: Int, c3: MyClass, src: File) extends A 

怎樣在性狀限定拷貝方法A所以它將匹配產生一個用於例類和「目標'檔案？鑑於定義確實typecheck和抱怨丟失的方法副本類B和C.

Answer 1

scala編譯器將不會生成複製方法的case類定義方法與名稱副本。

scala -Xprint:typer -e "sealed trait A { def copy[T <: A](s: String):T }; case class B(x: Int, y:Int) extends A" 

輸出：

/var/folders/fm/fm4b21vj6jl995ywlrd99t49tjthjc/T/scalacmd3413244935208502669.scala:1: error: class B needs to be abstract, since method copy in trait A of type [T <: this.A](s: String)T is not defined 
sealed trait A { def copy[T <: A](s: String):T }; case class B(x: Int, y: Int) extends A 
                  ^
one error found 
[[syntax trees at end of      typer]] // scalacmd3413244935208502669.scala 
package <empty> { 
    object Main extends scala.AnyRef { 
    def <init>(): Main.type = { 
     Main.super.<init>(); 
    () 
    }; 
    def main(argv: Array[String]): Unit = { 
     val args: Array[String] = argv; 
     { 
     final class $anon extends scala.AnyRef { 
      def <init>(): anonymous class $anon = { 
      $anon.super.<init>(); 
      () 
      }; 
      sealed abstract trait A extends scala.AnyRef { 
      def copy[T >: Nothing <: this.A](s: String): T 
      }; 
      case class B extends AnyRef with this.A with Product with Serializable { 
      <caseaccessor> <paramaccessor> private[this] val x: Int = _; 
      <stable> <caseaccessor> <accessor> <paramaccessor> def x: Int = B.this.x; 
      <caseaccessor> <paramaccessor> private[this] val y: Int = _; 
      <stable> <caseaccessor> <accessor> <paramaccessor> def y: Int = B.this.y; 
      def <init>(x: Int, y: Int): this.B = { 
       B.super.<init>(); 
      () 
      }; 
      override <synthetic> def productPrefix: String = "B"; 
      <synthetic> def productArity: Int = 2; 
      <synthetic> def productElement(x$1: Int): Any = x$1 match { 
       case 0 => B.this.x 
       case 1 => B.this.y 
       case _ => throw new IndexOutOfBoundsException(x$1.toString()) 
      }; 
      override <synthetic> def productIterator: Iterator[Any] = runtime.this.ScalaRunTime.typedProductIterator[Any](B.this); 
      <synthetic> def canEqual(x$1: Any): Boolean = x$1.$isInstanceOf[this.B](); 
      override <synthetic> def hashCode(): Int = { 
       <synthetic> var acc: Int = -889275714; 
       acc = Statics.this.mix(acc, x); 
       acc = Statics.this.mix(acc, y); 
       Statics.this.finalizeHash(acc, 2) 
      }; 
      override <synthetic> def toString(): String = ScalaRunTime.this._toString(B.this); 
      override <synthetic> def equals(x$1: Any): Boolean = B.this.eq(x$1.asInstanceOf[Object]).||(x$1 match { 
    case (_: this.B) => true 
    case _ => false 
}.&&({ 
       <synthetic> val B$1: this.B = x$1.asInstanceOf[this.B]; 
       B.this.x.==(B$1.x).&&(B.this.y.==(B$1.y)).&&(B$1.canEqual(B.this)) 
      })) 
      }; 
      <synthetic> private object B extends scala.runtime.AbstractFunction2[Int,Int,this.B] with Serializable { 
      def <init>(): this.B.type = { 
       B.super.<init>(); 
      () 
      }; 
      final override <synthetic> def toString(): String = "B"; 
      case <synthetic> def apply(x: Int, y: Int): this.B = new B(x, y); 
      case <synthetic> def unapply(x$0: this.B): Option[(Int, Int)] = if (x$0.==(null)) 
       scala.this.None 
      else 
       Some.apply[(Int, Int)](Tuple2.apply[Int, Int](x$0.x, x$0.y)); 
      <synthetic> private def readResolve(): Object = $anon.this.B 
      } 
     }; 
     { 
      new $anon(); 
     () 
     } 
     } 
    } 
    } 
}