Collections of concept types

[dawkot]

Would be nice if this was possibe:

type ShowableRef = concept x
    x is ref any #or x.sizeof == `bytes`
    x.`$` is string

var xs = newSeq[ShowableRef]()

[Yardanico]

Concepts are a compile-time thing, how it will work?
However this probably will be possible with vtref concepts, but they're not available yet

[zah]

Something similar to this will be possible with the "VTable Types" in the future.

Otherwise, there should be an error indicating that ShowableRef is not a concrete type in this particular situation (let's keep the issue open until this is implemented).