https://issues.dlang.org/show_bug.cgi?id=12718

          Issue ID: 12718
           Summary: Allow use invariant without parentheses or improve
                    error message
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: DMD
          Assignee: nobody@puremagic.com
          Reporter: temtaime@gmail.com

class C {
invariant {}
}

Error: use 'immutable' instead of 'invariant'

I think invariants should be allowed without parentheses or error message should say about it.

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