Re: [boost] [Interval] Conversion from integer types?

From: Neil Groves (neil_at_[hidden])
Date: 2008-01-04 10:26:47

I agree that the examples you provide appear safe. While proof by analogy is
fraud, it appears to be similar in nature to casts in general. One can
provide many examples of the safe use of casts, but generally avoidance
leads to better code.

I am not familiar enough with the use of boost::interval to take a strong
stance, espcially since I do not have metrics to back up my statements. I
would urge careful analysis incase the interoperability of types introduces
new risks.

In the case of template functions where you have template<class T> T foo(T
x) { return x -= 1; }, I like to use (when I remember!) boost::numeric_cast
since T might be smaller than int. That is, template<class T> T foo(T x) {
return x -= numeric_cast<T>(1); }

I think I'm probably being pedantic but as I recall the size of int is not
stated as part of the C++ specification, only in relative terms to other
types. Therefore mixing ints with floating-point types is not guaranteed to
be lossless, although on most implementations it will be.

I am certainly would concede to those developers that have more experience
with this library however, especially if they are doing the work!

HTH,
Neil Groves

On Jan 4, 2008 2:01 PM, John Maddock <john_at_[hidden]> wrote:

> Neil Groves wrote:
> > Are you certain that mixing floating-point types and integral types is
> > desirable?
> >
> > floating-point types are, of course, approximations unlike integer
> > types. It
> > is dangerous to mix the two, and the approach to do so should not be
> > allowed
> > even by a policy. Mixing floating point types with integer types
> > implicitly
> > is a poor software engineering practice without merit in my humble
> > opinion.
> >
> > Implicit type conversion has been a frequently regretted design
> > decision in
> > my experience despite the initial syntactic appeal.
>
> What do you consider is wrong with using integer literals to represent
> constants, where those constants are indeed integers?
>
> Either in code such as:
>
> my_real -= 1;
>
> or in tables of (integer) coefficients to polynomials?
>
> In this case my_real is a template type, so the conversion may or may not
> loose precision depending upon the type, but the since result is always
> represented as the floating point type, then there is no more accurate way
> to represent an integer than as an... integer.
>
> Converting the other way most certainly is wrong, of course.
>
> All IMHO,
>
> Regards, John.
>
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