Error using Specs2 with FluentLenium Api

问题:

I use Scala 2.10, Specs2 13.1-SNAPSHOT and the FluentLenium Api provided by Play2 Framework 2.1.

I have this line of code in my IntegrationSpec file, finding a child element (according to FluentLenium spec):

browser.find(".myClass").find("#mySubElement") must haveSize(1)

That line leads to the following compilation error:

error: type mismatch;
found   : org.fluentlenium.core.domain.FluentList[_ <: org.fluentlenium.core.domain.FluentWebElement]
required: org.fluentlenium.core.domain.FluentList[?0(in value $anonfun)] where type ?0(in value $anonfun) <: org.fluentlenium.core.domain.FluentWebElement
Note: org.fluentlenium.core.domain.FluentWebElement >: ?0, but Java-defined class FluentList is invariant in type E.
You may wish to investigate a wildcard type such as `_ >: ?0`. (SLS 3.2.10)

Is it a kind of...incompatibilty Scala/Java due to generics?? or a normal behaviour that I didn't figure out?

This line however (omitting any matcher), well compiles:

browser.find(".myClass").find("#mySubElement")

回答1:

The haveSize matcher require the element being matched to have an org.specs2.data.Sized typeclass in scope. The corresponding typeclass for java collections is:

implicit def javaCollectionIsSized[T <: java.util.Collection[_]]: Sized[T] = 
  new Sized[T] {
    def size(t: T) = t.size()
  }

I suspect that type inference here is the issue and you could try to tame it with the following ugly code:

browser.find(".myClass").
        find("#mySubElement").
        asInstanceOf[FluentList[FluentWebElement]] must haveSize(1)

Or maybe

browser.find(".myClass").
        find("#mySubElement").
        asInstanceOf[Collection[_]] must haveSize(1)

Or

import scala.collection.convert.JavaConverters._

browser.find(".myClass").
        find("#mySubElement").
        asScala must haveSize(1)