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: Deane Yang (deane.yang_at_[hidden])
Date: 2008-12-03 08:49:12

Edward Diener wrote:
> Mathias Gaunard wrote:
>> 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.

I have an even more extreme view on this. I don't believe any arithmetic 
operations should be permitted for constrained numbers. They just don't 
make sense (would you ever want to add two different days of a month?). 
There are occasions where you do want to perform an algorithm that does 
make sense but where arithmetic operations are performed along the way. 
But in those cases I want to be forced to do an explicit cast to an 
unconstrained type.

I would add that I think the concept of constrained values is tightly 
linked to the concept of units (by which I mean the concept of wrapping 
a number type by a meaningful type), as well as the concept of an 
algebraic type (where you constrain the algebraic operations that can be 
performed). I would love to see someone put this all together into a 
single coherent library.