在Scala中将模式匹配用于Ordered.compare
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我有以下Scala课程：
case class Person(firstName: String, lastName: String, age: Int)
extends Ordered[Person] {
def compare(that: Person): Int = {
if (this.lastName < that.lastName) -1
else if (this.lastName > that.lastName) 1
else if (this.firstName < that.firstName) -1
else if (this.firstName > that.firstName) 1
else this.age compare that.age
}
}
case class Person(firstName: String, lastName: String, age: Int)
extends Ordered[Person] {
def compare(that: Person): Int = {
that match {
case Person(_, thatLastName, _) if this.lastName < thatFile => -1
case Person(_, thatLastName, _) if this.lastName > thatFile => 1
case Person(thatFirstName, _, _) if this.firstName < thatFirstName => -1
case Person(thatFirstName, _, _) if this.firstName > thatFirstName => 1
case Person(_, _, thatAge) => this.age compare thatAge
}
}
}
Ordering[A]
implicit val personOrdering = new Ordering[Person] {
def compare(first: Person, second:Person): Int = {
second match {
case Person(_, thatLastName, _) if first.lastName < thatLastName => -1
case Person(_, thatLastName, _) if first.lastName > thatLastName => 1
case Person(thatFirstName, _, _) if first.firstName < thatFirstName => -1
case Person(thatFirstName, _, _) if first.firstName > thatFirstName => 1
case Person(_, _, thatAge) => first.age compare thatAge
}
}
}
case class Person(firstName: String, lastName: String, age: Int)
second
没有找到相关结果
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1 个回复
蹄渭信妥扳
s，它们不能保证为-1，0，1。Haskell's解决方案可以返回“枚举”对象（LT， EQ，GT）更清晰，可与模式匹配，但出于兼容性原因，Scala似乎遵循了C ++ / Java传统。 当然，您可以推出自己的比较“框架”：abstract sealed class CompResult(val toInt:Int) { def andThen(next: => CompResult): CompResult } case object LT extends CompResult(-1) { def andThen(next: => CompResult) = LT } case object EQ extends CompResult(0) { def andThen(next: => CompResult) = next } case object GT extends CompResult(1) { def andThen(next: => CompResult) = GT } implicit def int2Comp(n:Int) = if (n == 0) EQ else if (n < 0) LT else GT ((\"sdkfhs\" compareTo \"fldgkjdfl\"):CompResult) match { case LT => println(\"less\") case EQ => println(\"same\") case GT => println(\"more\") }case class Person(firstName: String, lastName: String, age: Int) extends Ordered[Person] { def compare(that: Person): Int = { (this.lastName compareTo that.lastName). andThen (this.firstName compareTo that.firstName). andThen (this.age compare that.age).toInt } }