Streaming and StreamingT extend Product with Serializable

[ceedubs]

This helps type inference by fixing the least upper bound of subtypes of
Streaming(T).

Before:

scala> val x = if (true) Cons(1, Now(Streaming.empty[Int])) else Streaming.Empty[Int]()
x: Product with Serializable with cats.data.Streaming[Int] = Streaming(1, ...)

After:

scala> val x = if (true) Cons(1, Now(Streaming.empty[Int])) else Streaming.Empty[Int]()
x: cats.data.Streaming[Int] = Streaming(1, ...)

[hakuch]

Off-topic comment: There was a brief conversation on the Gitter channel on the need to explicitly inherit from Product and Serializable in the base trait or class when the sub-classes are case classes in order to produce a more helpful "least upper-bound". I wish there was first-class support in Scala for algabraic data types like in Haskell or OCaml. Do intersection types in Dotty address this?

[codecov-io]

Current coverage is 77.19%

Merging #648 into master will not affect coverage as of 1652b4a

@@            master    #648   diff @@
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  Stmts         2083    2083       
  Branches        70      70       
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  Hit           1608    1608       
  Partial          0       0       
  Missed         475     475       

Review entire Coverage Diff as of 1652b4a

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[ceedubs]

@hakuch That's an interesting question. I haven't really read up on Dotty yet. Someone else might have an answer for that.

[fthomas]

👍

[stew]

👍