The state of string interpolation

[Paul Backus]

On Saturday, 8 December 2018 at 19:17:26 UTC, Martin Tschierschke 
wrote:
> I am referring to this post, because it is the first mentioning 
> the mixin way in this thread:
>
>           Why is mixin() not allowed in UFCS?

Because mixin isn't a function, it's a special type of expression 
(like `sizeof` is in C). UFCS only applies to functions.

Here's the relevant part of the language specification: 
https://dlang.org/spec/expression.html#mixin_expressions