On Friday, 2 August 2019 at 21:10:08 UTC, Andrej wrote:
The D spec mentions something called mixin types:
This is brand new to the spec and hasn't yet been released in a compiler.
You can get a nightly build here https://dlang.org/changelog/pending.html to maybe try, but I don't think it will be in a proper release until ... my guess is Sept 1.