Length

Supertrait for Length type classes.

This traits enable you to use ScalaTest matchers' “have length” syntax to be used with arbitrary objects. As an example, consider java.net.DatagramPacket, which has a getLength method. By default, this can't be used with ScalaTest's have length syntax.

scala> import java.net.DatagramPacket
import java.net.DatagramPacket

scala> import org.scalatest.matchers.ShouldMatchers._
import org.scalatest.matchers.ShouldMatchers._

scala> val dp = new DatagramPacket(Array(0x0, 0x1, 0x2, 0x3), 4)
dp: java.net.DatagramPacket = java.net.DatagramPacket@54906181

scala> dp.getLength
res0: Int = 4

scala> dp should have length 4
:13: error: could not find implicit value for parameter ev: org.scalatest.matchers.ShouldMatchers.Extent[java.net.DatagramPacket]
         dp should have length 4
            ^

scala> implicit val lengthOfDatagramPacket =
    |   new Length[DatagramPacket] {
    |     def extentOf(dp: DatagramPacket): Long = dp.getLength
    |   }
lengthOfDatagramPacket: java.lang.Object with org.scalatest.matchers.ShouldMatchers.Length[java.net.DatagramPacket] = $anon$1@550c6b37

scala> dp should have length 4

scala> dp should have length 3
org.scalatest.exceptions.TestFailedException:  java.net.DatagramPacket@54906181 had length 4, not length 3