handling T.min the right way

[Don Clugston]

Andrei Alexandrescu (See Website For Email) wrote:
> Don Clugston wrote:
>> Andrei Alexandrescu (See Website For Email) wrote:
>>> A while ago, C++ did the mistake of defining 
>>> std::numeric_limits<T>::min() with a different semantics for 
>>> floating-point types than for integral types. That hurt generic 
>>> numeric code a lot.
>>>
>>> D has taken over the same mistake: T.min means the smallest value of 
>>> the type, except for floating-point types, where it means the 
>>> smallest positive value.
>>>
>>> The right way is to have T.min always return the minimum value (duh) 
>>> and define a separate property T.min_positive.
>>>
>>> The question is, would a lot of code be hurt by such a change?
>>>
>>>
>>> Andrei
>>
>> It probably wouldn't break a huge amount of D code, but I don't think 
>> there would be many cases where T.min for a floating point type would 
>> be useful. More significant is the problems involved in converting 
>> from C or Fortran code to D.
> 
> I'm not even discussing the utility of min_positive. All I'm saying is 
> that if you say "min", you should return "min", particularly when others 
> do exactly that.
> 
>> On a more profound level...
>> I'm not aware of many cases where it's possible to treat integer and 
>> floating-points generically. People often try, but usually the code is 
>> incorrect for the floating point types, since the semantics are 
>> completely different. (For example, I don't know why x++ is legal for 
>> floating point types; I think it's just a newbie trap; you have no 
>> guarantee that x++ is different to x).
>>
>> What type of generic numeric code did you have in mind? What are the 
>> benefits which would come by such a change?
> 
> Trivially simple: the min and max functions. For min, the code picks the 
> type with the smallest .min. For max, the code picks the type with the 
> largest .max.

Obviously, but are there many other functions like that? Also, you 
really should treat floating point as a special case, anyway, because of 
the possibility of a NaN.

I'd be surprised if the total benefit amounted to more than a few dozen 
lines of library code.

There's also the issue of complex types. Currently, this passes:

static assert(creal.max == real.max+1i*real.max);

-- which is a little strange.