[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 #11 from Kenji Hara <k.hara.pg at gmail.com> ---
(In reply to Temtaime from comment #10)
> @Kenji it's useless imo.

My main concern is, that disallowing current invariant() syntax will break many
existing D2 code. I'm afraid to decrease language stability.

On the other hand, accepting the syntax `unittest(){...}` would not have any
design benefit, but it will increase syntax consistency.

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