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, the following Bridge class:
scala> import org.scalatest._
import org.scalatest._
scala> import enablers.Length
import enablers.Length
scala> import Matchers._
import Matchers._
scala> case class Bridge(span: Int)
defined class Bridge
Out of the box you can't use the should have length syntax with Bridge,
because ScalaTest doesn't know that a bridge's span means its length:
scala> val bridge = new Bridge(2000)
bridge: Bridge = Bridge(2000)
scala> bridge should have length 2000
<console>:34: error: could not find implicit value for
parameter len: org.scalatest.enablers.Length[Bridge]
bridge should have length 2000
^
You can teach this to ScalaTest, however, by defining an implicit Length[Bridge].
scala> implicit val lengthOfBridge: Length[Bridge] =
| new Length[Bridge] {
| def lengthOf(b: Bridge): Long = b.span
| }
lengthOfBridge: org.scalatest.enablers.Length[Bridge] = $anon$1@3fa27a4a
With the implicit Length[Bridge] in scope, you can now use ScalaTest's should have length
syntax with Bridge instances:
scala> bridge should have length 2000
res4: org.scalatest.Assertion = Succeeded
scala> bridge should have length 2001
org.scalatest.exceptions.TestFailedException: Bridge(2000) had length 2000 instead of expected length 2001
at org.scalatest.MatchersHelper$.newTestFailedException(MatchersHelper.scala:148)
at org.scalatest.MatchersHelper$.indicateFailure(MatchersHelper.scala:366)
at org.scalatest.Matchers$ResultOfHaveWordForExtent.length(Matchers.scala:2720)
... 43 elided
Supertrait for
Length
typeclasses.Trait
Length
is 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 length
syntax. In other words, this trait enables you to use the length checking syntax with arbitrary objects. As an example, the followingBridge
class:Out of the box you can't use the
should have length
syntax withBridge
, because ScalaTest doesn't know that a bridge's span means its length:You can teach this to ScalaTest, however, by defining an implicit
Length[Bridge]
.With the implicit
Length[Bridge]
in scope, you can now use ScalaTest'sshould have length
syntax withBridge
instances: