Add the tuples PR

Author: anatoliykmetyuk

docs/blog/_posts/2020-06-16-25th-dotty-milestone-release.md

@@ -1,12 +1,12 @@
 ---
 layout: blog-page
-title: Announcing Dotty 0.25.0-RC2 - speed-up of givens
+title: Announcing Dotty 0.25.0-RC2 - speed-up of givens and change in the tuple API
 author: Anatolii Kmetiuk
 authorImg: /images/anatolii.png
 date: 2020-06-16
 ---
 
-Hello! We are excited to announce 0.25.0-RC2 of Dotty. In this version, following feedback of the community, we have improved compilation speeds when programming with givens. We have also made progress towards better cross-compilation of macro definitions between Scala 2 and Scala 3.
+Hello! We are excited to announce 0.25.0-RC2 of Dotty. In this version, following feedback of the community, we have improved compilation speeds when programming with givens. We have also made some improvements to the tuple API.
 
 You can try out this version right now, from the comfort of your SBT, by visiting the [home page](https://dotty.epfl.ch/) and scrolling down to the "Create a Dotty Project" section.
 
@@ -15,6 +15,17 @@ Alternatively, you can try this version of Scala online via [Scastie](https://sc
 Enjoy the ride🚀!
 
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+# Dedicated type for empty tuples
+We have added a type `EmptyTuple` to represent empty tuples. Previously empty tuples were represented by `Unit`. This change was done so that all the tuples are a subtype of `Product`. Now, tuples have the following type hierarchy:
+
+```scala
+Product -- Tuple -+- EmptyTuple
+                  |
+                  +- NonEmptyTuple -- *:[Head, Tail <: Tuple]
+```
+
+This change impacts existing typeclass derivation codebases in that they now should use `EmptyTuple` instead of `Unit` in the tuple context.
+
 # Avoid excessive slowdowns when suggesting missing imports in error messages
 Dotty brings to the user an enhanced error reporting when it comes to programming with givens. This better error reporting, however, proved to be a trade-off. Sometimes it takes an unreasonable amount of time and space to compute a quality suggestion to the end user.