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Tags should be covariant

Open Atry opened this issue 8 years ago • 2 comments

The current tag is @@[A, T], which is invariant. As a result, ParallelFuture[String] is not a ParallelFuture[Any], even if Future[String] is a Future[Any].

Is it possible to change the signature to @@[+A, T]?

Atry avatar May 12 '17 05:05 Atry

I think we decided a while ago that variance isn't worth the cost in scalaz.

puffnfresh avatar May 12 '17 06:05 puffnfresh

What's the cost?

Atry avatar May 12 '17 06:05 Atry