handling T.min the right way

[Lars Ivar Igesund]

Andrei Alexandrescu (See Website For Email) wrote:

> Don Clugston wrote:
>> 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.
> 
> There was another example (computing the minimum of a nonempty
> collection). But to me the issue is a tad different: (1) the name is
> clearly misused; (2) it's easy to fix; (3) not fixing it sends the wrong
> message ("we carried over whatever was in C++ on numerics").

And what about carrying over that const mess from C++? If const as a keyword
is to stay - just let it mean constant - nothing else.

> D takes 
> pride in taking care of minutiae. It's odd to have the smorgasbord of
> floating-point operators that D has (how often did _you_ use !<>=?) yet
> at the same time say, "oh, min? that's not really min. I was kidding."

!<>= is in use in Tango as it seems to what is actually happening when
looking for NaN :)

-- 
Lars Ivar Igesund
blog at http://larsivi.net
DSource, #d.tango & #D: larsivi
Dancing the Tango