ambiguous implicit values when matching on Future[Set[T]]

[swar30]

Hi, i'm using org.specs2:specs2_2.10:2.3.12 in Scala and I have this expression

(someList:Future[Seq[_]]) must haveSize(1).await

Which results in compilation error

Error:(64, 52) ambiguous implicit values:
both method scalaTraversableIsSized in trait TraversableBaseMatchers of type [I <: scala.collection.GenTraversableOnce[_]]=> org.specs2.data.Sized[I]
and method scalaArrayIsSized in trait TraversableBaseMatchers of type [T]=> org.specs2.data.Sized[Array[T]]
match expected type org.specs2.data.SizedT must haveSize(1).await
^

I'm new to Scala, but this seems like a bug in implicit definitions

[etorreborre]

That's an unfortunate interaction between several implicits + type inference. I'm going to see if I can fix this.

[swar30]

Thanks, if it's hard to resolve, may be it makes sense to add docs that
explain the work around (explicit casting), I'm new to Scala so for me it
was really hard to work around this easily.
I ended up with

someListFuture must haveSizeList[_].await;

[etorreborre]

In the meantime you can use an annotation:

(someList:Future[Seq[_]]) must haveSize[Seq[_]](1).await

[etorreborre]

I tried to fix this but the way type inference works and given the existing constraints on haveSize, I couldn't find a solution that was not involving annotating the type on haveSize. So I added this information to the User Guide.

[swar30]

Thanks

On Tue, Aug 19, 2014 at 2:55 AM, Eric Torreborre notifications@github.com
wrote:

I tried to fix this but the way type inference works and given the
existing constraints on haveSize, I couldn't find a solution that was not
involving annotating the type on haveSize. So I added this information to
the User Guide.

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Reply to this email directly or view it on GitHub
#289 (comment).

Thanks,
Alex Shnayder
Wix Cloud, Wix.com