The 4th Edition Upgrade Companion is now available.
A version of the Upgrade Companion (a document for 4th Edition readers who are excited to learn the new C# 10 features as you go) is available here: Upgrade Companion for 4th Edition
A version of the Upgrade Companion (a document for 4th Edition readers who are excited to learn the new C# 10 features as you go) is available here: Upgrade Companion for 4th Edition