how is this array subtyping inside struct (bug?) possible?

[Dominikus Dittes Scherkl]

On Tuesday, 11 August 2020 at 13:36:19 UTC, Simen Kjærås wrote:
> So how should writeln deal with input ranges?

I would expect writeln to first try to use some const-interface 
(e.g. indexing if the given type provides that). Only if such 
interface is not available, it should try modifying interfaces 
like range pop-front.