[Issue 20328] [REG 2.089 beta] deprecation message about Nullable.get in isInputRange

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20328

--- Comment #6 from FeepingCreature <default_357-line at yahoo.de> ---
I realize it's a dirty no good very bad workaround, but the easiest way forward
may be to (temporarily!) explicitly handle Nullable in `isInputRange`. That or
walk back the `get` deprecation and do it via a transition switch instead? ... 

That or think a lot harder about how deprecations are supposed to work with
templated code, because this is very very much a general problem.

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