On Wednesday, 24 January 2018 at 14:22:59 UTC, Meta wrote: > One way we could probably improve the error message is to > change it to "template struct test.A(int var = 3) is used as a > type. It must be instantiated", or something along those lines, > to make it clear why you can't use A as a type. https://github.com/dlang/dmd/pull/7769