[Issue 9149] Disallow converting delegates to const

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=9149

--- Comment #15 from Sobirari Muhomori <dfj1esp02 at sneakemail.com> ---
If we have syntax to declare delegates with function attributes and
disambiguate context attributes, why not implement contravariance check? It's
likely to be big and complex, but it's pure, doesn't change the compiler state,
doesn't even allocate memory, only takes two const types and returns bool -
unlikely to cause serious side effects.

--