Trait Length is a typeclass trait for objects that can be queried for length.
Objects of type T for which an implicit Length[T] is available can be used
with the should have length syntax.
In other words, this trait enables you to use the length checking
syntax 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._
import org.scalatest.Matchers._
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 lengthOf(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
Supertrait for
Lengthtypeclasses.Trait
Lengthis a typeclass trait for objects that can be queried for length. Objects of type T for which an implicitLength[T]is available can be used with theshould have lengthsyntax. In other words, this trait enables you to use the length checking syntax with arbitrary objects. As an example, considerjava.net.DatagramPacket, which has agetLengthmethod. By default, this can't be used with ScalaTest'shave lengthsyntax.