Scala，部分函数

object ValidBigInt {
  def unapply(s: String): Option[Int] = {
    val bi = BigInt(s)
    if (bi.isValidInt) Some(bi.intValue) else None
  }
}

val toInt: PartialFunction[String, Int] = {
  case ValidBigInt(i) => i
}

case

val toInt = new PartialFunction[String, Int] {
  def isDefinedAt(s: String) = BigInt(s).isValidInt
  def apply(s: String) = BigInt(s).intValue
}

isDefinedAt

apply

Option[Int]

import scala.util.control.Exception._

scala> def fn(s: String) = catching(classOf[NumberFormatException]) opt {BigInt(s)}
fn: (s: String)Option[scala.math.BigInt]

scala> val fnPf = Function.unlift(fn)
fnPf: PartialFunction[String,scala.math.BigInt] = <function1>

scala> val fn = fnPf.lift
fn: String => Option[scala.math.BigInt] = <function1>

scala> import PartialFunction._
import PartialFunction._

scala> cond(\"abc\") { case \"def\" => true }
res0: Boolean = false

scala> condOpt(\"abc\") { case x if x.length == 3 => x + x }
res1: Option[java.lang.String] = Some(abcabc)

PartialFunction

object pf extends PartialFunction[Int,String] {
  def isDefinedAt(in: Int) = in % 2 == 0

  def apply(in: Int) = {
    if (in % 2 == 0) 
      \"even\" 
    else 
      throw new MatchError(in + \" is odd\")
}

import java.lang.NumberFormatException
import scala.util.control.Exception._

val toInt: PartialFunction[String, Int] = {
  catching(classOf[NumberFormatException]) opt BigInt(_) match {
    case Some(bi) if bi.isValidInt => bi.intValue
  }
}

val toInt: PartialFunction[String, Int] = (s: String) => BigInt(s) match {
  case bi if bi.isValidInt => bi.intValue
}