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