Value Preservation and Polysemy -> context dependent integer literals

[Andrei Alexandrescu]

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