https://issues.dlang.org/show_bug.cgi?id=20076
--- Comment #1 from Ethan Watson <[email protected]> --- More digging makes me think instead that because I'm using class objects, it actually needs a const-removing cast. And since it's not there, it's silently assuming the alias this is the correct thing to use. So I can deal with it now at least, but that error message is another case of "Confusing D error message" --
