Re: [boost] Checked Integral Class

From: michael toksvig (michaeltoksvig_at_[hidden])
Date: 2005-09-15 14:40:30

also, the type of a binary operator's return value should combine the 
intervals of the operands

e.g. given:
    CheckedIntegralValue<int, -10, 100> a;
    CheckedIntegralValue<int, -100, 20> b;

then the type of a+b should be CheckedIntegralValue<int, -110, 120>

and given:
    CheckedIntegralValue<int, -110, 120> sum;

then sum = a+b, sum = a, and sum = b should all compile just fine

conversely, a = sum, b = sum, and a = b should not

this may have been implied, just wanted to make sure

regards,

/michael toksvig

"Dan McLeran" <dan.mcleran_at_[hidden]> wrote in message 
news:dga6uu$c6j$1_at_sea.gmane.org...
>I like the idea of having the response to the over/under range condition 
>configurable. Maybe a policy class could handle what to do in that 
>situation? I guess I got a little tunnel vision trying to emulate what Ada 
>does in response to an invalid assignment, which is raise Constraint_Error.
>
> I agree that this does not emulate exactly what is possible in Ada, but I 
> liked the idea of being able to specify that a type can only hold a 
> specific range of values.
>
> "Maciej Sobczak" <prog_at_[hidden]> wrote in message 
> news:43289177.9030904_at_msobczak.com...
>> Hi,
>>
>> Dan McLeran wrote:
>>> I've written a template class to hold a range of valid integral values. 
>>> My
>>> intent was to mimic Ada's ability to define a type like this:
>>>
>>> type SmallInt is range -10 .. 10;
>>>
>>> One can then declare objects of this type and any subsequent assignment 
>>> that
>>> violated this range constraint woud throw an exception.
>>
>> Careful with that. This approach, in my humble opinion, is very limited.
>> Why do you assume that exception is The Right Thing when the out of
>> bound condition is detected?
>>
>> These are things that I would like to have, *depending on situation*:
>>
>> 1. throw some exception (this is what you have)
>>
>> 2. abort immediately without doing *anything* (note that exception
>> causes some code to be executed, like destructors of automatic objects -
>> I might want to avoid this and just kill the program immediately)
>>
>> 3. wrap the result (kind of modulo arithmetic, but more general because
>> allowing to have the lower bound different than 0 - say that if the
>> range is 10..20 then 23 should be wrapped to be 13)
>>
>> 4. saturate the result (if you have the range 0..100 and the result of
>> some computation is 150, cut it to 100 and continue with it) - actually,
>> saturated arithmetic is very convenient, for example in signal processing
>>
>> 5. actually allow the out-of-range value, but log that fact somewhere or
>> send me an e-mail, etc.
>>
>> 6. ...
>>
>>
>> I leave the list open, beacuse it is clear that the library itself
>> should be customizeable in this regard.
>>
>>
>> More to this - the bare checked class is not really emulating what Ada
>> supports. What about this (Ada):
>>
>> type SmallInt is range -10 .. 10;
>> subtype EvenSmallerInt is SmallInt range -5 .. 5;
>>
>> Now, you can use EvenSmallerInt wherever SmallInt is expected, because
>> one is a subtype of another. Ada does not allow multiple supertypes,
>> although that is a logical extension of the idea, quite useful in my
>> opinion and worth to have.
>>
>>
>> You will find a very sketchy and incomplete implementation of all these
>> ideas at:
>>
>> <http://www.msobczak.com/prog/bin/safetypes.tar.gz> (3kB)
>>
>>
>> -- 
>> Maciej Sobczak : http://www.msobczak.com/
>> Programming    : http://www.msobczak.com/prog/
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