[Issue 10326] Disallow 'invariant' for immutable, allow class/struct invariants without (), and later disallow usage of ()

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=10326

--- Comment #12 from Temtaime <temtaime at gmail.com> ---
I think we should simply show deprecate message for invariant() to help
updating user's code and remove it in future.
It's best way imo.

--