Re: [Boost-users] [review][constrained_value] Review of Constrained Value Library begins today

Subject: Re: [Boost-users] [review][constrained_value] Review of Constrained Value Library begins today
From: Edward Diener (eldiener_at_[hidden])
Date: 2008-12-03 08:32:17

Mathias Gaunard wrote:
> Jeff Garland wrote:
> 
>>       bounded_int<int, 0, 23>::type hour;
>>       hour = 20; // OK
>>       hour = 26; // exception!
>>
>> Behavior in case of assignment of an invalid value can be customized. 
> 
> I think this is wrong.
> Providing an invalid value should be a non-recoverable programming error.
> Non-recoverable means it should abort the program, and programming error 
> means it should only be enabled in debug mode.
> i.e. an assert is the best choice to assert the preconditions are met.

I disagree with your analysis. The '26' value could be a run-time 
calculation and not just a compile-time constant. In which case you are 
saying that the assignment of a run-time calculation should assert only 
when run in debug mode and otherwise should be ignored. I can not agree 
with that idea.

> 
> Apart from that, wouldn't it be more interestin, when multiplying a 
> bounded_int<int, 0, 23> by 2, to yield a bounded_int<int, 0, 46> instead 
> of attempting to keep the object with the same constraint?
> Of course, that only works with bounded_int and not constraints in general.

I disagree with this also. The entire idea of a constraint in this 
library is that the underlying value meets the criteria of the 
constraint and not that the constraint changes to accomodate a new 
underlying value.