double.init is real.nan, is it a bug?

[bsd]

On Thursday, 15 August 2013 at 05:12:35 UTC, Jonathan M Davis 
wrote:
> On Thursday, August 15, 2013 06:01:21 bsd wrote:
>> Hi all,
>> 
>
> There are multiple values for NaN. It's still a bit surprising 
> to me that
> assert(val is double.nan) failed, but as long as val is still 
> one of the
> values for NaN, it shouldn't matter. It wouldn't have been at 
> all suprising
> though if you had two different NaNs which were generated 
> through arithmetic
> which didn't match. In general, you can't rely on the bit 
> pattern for NaN.
>
>> I also found this confusing:
>> ---
>> void main() {
>> 
>>      assert(double.init is double.nan); // passes expected
>> 
>>      assert(double.init is float.init); // passes, unexpected
>>      assert(double.init is real.init); // passes, unexpected
>> 
>>      assert(double.init is real.nan); // passes, unexpected
>>      assert(double.init is float.nan); // passes, unexpected
>> 
>> }
>> ---
>> I don't think these should be passing...should they??
>
> To do the comparison, the same size types must be compared, so 
> the smaller
> floating point types are promoted to the larger type in the 
> expression, and
> evidently, promoting the init value of a smaller floating point 
> value gives you
> the same value as the init value of the larger floating point 
> value.
>
> - Jonathan M Davis

This explains why (double.nan is float.nan) && (double.nan is 
real.nan). I understand that now, thanks.

I found std.math.isNaN in just after I posted, I really should 
read the docs first :D

For some reason I thought ('var' is double.nan) did this isNaN 
check, sort of like (key in AA) ... but 'in' is in and 'is' is, 
well, just is.

Thanks for the help.