[Issue 13420] double.nan unusable as AA key

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=13420

--- Comment #6 from Vladimir Panteleev <thecybershadow at gmail.com> ---
Maybe the AA implementation should assert that keys added to it should be equal
to themselves. That would make the problem easier to spot, at least (in my case
it caused the output to be incorrect).

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