Re: [boost] [chrono/date] validated versus valid dates

Subject: Re: [boost] [chrono/date] validated versus valid dates
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2013-05-06 05:40:26

Le 06/05/13 00:21, Rob Stewart a écrit :
> On May 5, 2013, at 4:01 PM, "Vicente J. Botet Escriba" <vicente.botet_at_[hidden]> wrote:
>
>> Allowing to build dates that are not validated doesn't mean that they are not valid. A validated date is always valid. E.g
>>
>>   date d(year(2013), may, day(5));
>>
>> d is not a validated date but is valid.
>>
>> Having a is_validated() function in addition to is_valid() could have its uses
>>
>>   assert(  ! d.is_validated() && d.is_valid()  );
>>
>> is_validated() function forces to use a bit to store this information on the date representation, but it improves the performances of the is_valid() function.
>>
>> Moving from a possible unvalidated to a validated one would need
>>
>>   date d1;
>>   ...
>>   date d2(d1.year(), d1.month(), d1.day(), check);
>>
>> Instead of this a validate factory makes this clearer
>>
>>   date d1;
>>   ...
>>   date d2 = validate(d1);
>>
>>
>> date validate(date const& dt)
>> {
>>   if (dt.is_validated()) return *this;
>>   else if (dt.is_valid())
>>   {
>>     date res(dt);
>>     res.set_validated_(); // this is private
>>     return res;
>>   }
>>   throw bad_date();
>> }
> The basic idea is reasonable, but I suggest a couple of alternatives. First, I see no value in making is_validated() public. Second, validate() should return void:
>
> void
> date::validate()
> {
>     if (!is_valid())
>     {
>        throw bad_date();
>     }
> }
>
> bool
> date::is_valid()
> {
>     if (validated())
>     {
>        return true;
>     }
>     // do validation
>     if (valid)
>     {
>        validated_ = true;
>     }
>     return valid;
> }
>
> Usage:
>
> date d1;
> d1.validate(); // throws bad_date
> date d2(year(2013), may, day(5));
> d2.validate();
> assert(d2.is_valid());
>
>
>
I thought about this alternative. As is_valid must be const, this 
request validated_ to be mutable. I wanted to use one of the unused bits 
to store this information and I don't know if I can declare a bitfield 
mutable. Can I?

Best,
Vicente