floats default to NaN... why?

[F i L]

 From the FaQ:

> NaNs have the interesting property in that whenever a NaN is 
> used as an operand in a computation, the result is a NaN. 
> Therefore, NaNs will propagate and appear in the output 
> whenever a computation made use of one. This implies that a NaN 
> appearing in the output is an unambiguous indication of the use 
> of an uninitialized variable.

> If 0.0 was used as the default initializer for floating point 
> values, its effect could easily be unnoticed in the output, and 
> so if the default initializer was unintended, the bug may go 
> unrecognized.


So basically, it's for debugging? Is that it's only reason? If so 
I'm at loss as to why default is NaN. The priority should always 
be in the ease-of-use IMO. Especially when it breaks a "standard":

     struct Foo {
       int x, y;    // ready for use.
       float z, w;  // messes things up.
       float r = 0; // almost always...
     }

I'm putting this in .Learn because I'm not really suggesting a 
change as much as trying to learn the reasoning behind it. The 
break in consistency doesn't outweigh any cost of "debugging" 
benefit I can see. I'm not convinced there is any. Having core 
numerical types always and unanimously default to zero is 
understandable and consistent (and what I'm use too with C#). The 
above could be written as:

     struct Foo {
       float z = float.nan, ...
     }

if you wanted to guarantee the values are set uniquely at 
construction. Which seems like a job better suited for unittests 
to me anyways.

musing...