Value Preservation and Polysemy -> context dependent integer literals

[Fawzi Mohamed]

On 2008-12-05 07:02:37 +0100, Andrei Alexandrescu 
<SeeWebsiteForEmail at erdani.org> said:

> Sergey Gromov wrote:
>> Thu, 04 Dec 2008 09:54:32 -0800, Andrei Alexandrescu wrote:
>> 
>>> Fawzi Mohamed wrote:
>>>> On 2008-12-01 22:30:54 +0100, Walter Bright <newshound1 at digitalmars.com> said:
>>>> 
>>>>> Fawzi Mohamed wrote:
>>>>>> On 2008-12-01 21:16:58 +0100, Walter Bright <newshound1 at digitalmars.com> said:
>>>>>> 
>>>>>>> Andrei Alexandrescu wrote:
>>>>>>>> I'm very excited about polysemy. It's entirely original to D,
>>>>>>> I accused Andrei of making up the word 'polysemy', but it turns out it 
>>>>>>> is a real word! <g>
>>>>>> Is this the beginning of discriminating overloads also based on the 
>>>>>> return values?
>>>>> No. I think return type overloading looks good in trivial cases, but as 
>>>>> things get more complex it gets inscrutable.
>>>> I agreee that return type overloading can go very bad, but a little bit 
>>>> can be very nice.
>>>> 
>>>> Polysemy make more expressions typecheck, but I am not sure that I want that.
>>>> For example with size_t & co I would amost always want a stronger 
>>>> typechecking, as if size_t would be a typedef, but with the usual rules 
>>>> wrt to ptr_diff, size_t,... (i.e. not cast between them).
>>>> This because mixing size_t with int, or long is almost always 
>>>> suspicious, but you might see it only on the other platform (32/64 
>>>> bit), and not on you own.
>>>> 
>>>> Something that I would find nice on the other hand is to have a kind of 
>>>> integer literals that automatically cast to the type that makes more 
>>>> sense.
>>> Wouldn't value range propagation take care of that (and actually more)? 
>>> A literal such as 5 will have a support range [5, 5] which provides 
>>> enough information to compute the best type down the road.
>> 
>> It sounds very nice and right, except it's incompatible with Cee.
>> 
>> Well, you can safely reduce bit count so that assigning "1025 & 15" to
>> "byte" would go without both a cast and a warning/error.  But you cannot
>> grow bitcount beyond the C limits, that is, you cannot return long for
>> "1024 << 30."  You should probably report an error, and you should
>> provide some way to tell the compiler, "i mean it."
>> 
>> In the worst case, any shift, multiplication or addition will result in
>> a compiler error.  Do I miss something?
> 
> Well any integral value carries:
> 
> a) type as per the C rule
> 
> b) minimum value possible
> 
> c) maximum value possible
> 
> The type stays the type as per the C rule, so there's no change there. 
> If (and only if) a *narrower* type is asked as a conversion target for 
> the value, the range is consulted. If the range is too large, the 
> conversion fails.
> 
> Andrei

basically the implicit conversion rules of C disallowing automatic 
unsigned/signed conversions to unsigned?
Fawzi