Why do some T.init evaluate to true while others to false?

[Basile B. via Digitalmars-d-learn]

On Thursday, 26 May 2016 at 15:48:18 UTC, Basile B. wrote:
> On Thursday, 26 May 2016 at 15:34:50 UTC, ArturG wrote:
>> On Thursday, 26 May 2016 at 15:29:52 UTC, Basile B. wrote:
>>
>>>
>>> float.init is not equal to 0.0f. In D FP points values are 
>>> initialized to nan (not a number).
>>>
>>> By the way for strings it works, it's like the array case I 
>>> described in the first answer).
>>
>> yes i guess i tested all/most types and know that float.init 
>> is float.nan but why is nan true and not false?
>
> Oh, I'm so sorry ! I totally missed the point of the Q.
>
> float.nan is not a "unique" value. Several values verify "nan" 
> (Look at std.math.isNan). So I suppose it's simpler to test for 
> nullity. Though with the sign there's also two possible 0...

void main(string[] args)
{
     writeln(float.nan == float.init); // false
     import std.math: isNaN;
     writeln(isNaN(float.nan));  // true
     writeln(isNaN(float.init)); //true
}

So the shortcut in the compiler might be more simple, there is 
only a single test for "if(myFloat)"...