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 10:36:48

Deane Yang wrote:
> 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?).

You have chosen a particular type for which arithmetic operations 
sometimes make little sense. In many other situations this is not the case.

> 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.

It becomes inconvenient to use an explicit cast. It is more flexible 
that a constraint can transform to its underlying type whenever 
necessary, but still maintain the constraint after the operation occurs.

> 
> 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.

There is already a units library in 1.37. Perhaps you want constraints 
added to this library.