Maybe, but that really doesn't affect here, because this is druntime, and both `std.metastrings.Format` and `std.string.format` are in Phobos. There's a similar function in core.time for the same reason. But if we were certain that `sprintf` (or `sprintfn` or whatever)` is actually `pure`, then we might be able to add `pure` to its signature and and avoid this. I don't know if that'll work though, but we can remove this later if it does.