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[英]Scala: How to pattern-match the enclosing object of an inner case class?
[英]How to pattern-match a nested class in Scala?
我已经尝试了下面的代码(相同的方法是在Scala编程之后编写的 )
class Person() {
class Room(r: Int, c: Int) {
val row = r
val col = c
override def hashCode: Int =
41 * (
41 + row.hashCode
) + col.hashCode
override def equals(other: Any) =
other match {
case that: Room =>
(that canEqual this) &&
this.row == that.row &&
this.col == that.col
case _ => false
}
def canEqual(other: Any) =
other.isInstanceOf[Room]
}
val room = new Room(2,1)
}
val p1 = new Person()
val p2 = new Person()
println(p1.room == p2.room)
>>> false
经过一些分析后,我发现Scala为每个Person
实例重新定义了Class Room
,这就是两个房间不相等的原因。
解决问题的一种可能性是将类放在类Person
,但这并不总是最简单的。 (例如,如果类必须访问Person
某些参数。)
有什么选择来写同等方法?
问题是你的两个房间是路径依赖类型的实例:它们的类型是p1.Room
和p2.Room
:
scala> :type p1.room
p1.Room
实现此功能的一种方法是使用类型选择引用Room
,即Person#Room
。
class Person() {
class Room(r: Int, c: Int) {
val row = r
val col = c
override def hashCode: Int = // omitted for brevity
override def equals(other: Any) =
other match {
case that: Person#Room =>
(that canEqual this) &&
this.row == that.row &&
this.col == that.col
case _ => false
}
def canEqual(other: Any) =
other.isInstanceOf[Person#Room]
}
val room: Room = new Room(2,1)
}
val p1 = new Person()
val p2 = new Person()
scala> p1.room == p2.room
res1: Boolean = true
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