[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 #4 from Kenji Hara <k.hara.pg at gmail.com> ---
Remove errors and accept the syntax `invariant { ... }` for declaring invariant
block.
https://github.com/D-Programming-Language/dmd/pull/3540

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