Re: [boost] [Review:Algorithms] Order of args to clamp

Subject: Re: [boost] [Review:Algorithms] Order of args to clamp
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2011-09-26 14:01:15

Vicente J. Botet Escriba wrote:
> Le 26/09/11 13:36, Dave Abrahams a écrit :
> >
> > Note: you can solve that problem by asking the caller to do
> > the conversion ;-)
> >
> I'm not sure this could always be the desired interface for
> the caller. When I want to clip an 22 bit integer to a 16 bit
> integer, I expect the result be a 16 bit integer. So in these
> cases the result type will be the types of lo and hi.
>
>    int v;
>    short lo,hi;
>    short res= clamp(v, lo,hi);

How does the algorithm select the smaller return type when clamping to a limit, while selecting the larger return type otherwise?

> And in this case I can not convert the 22 bits integer to a 16
> bit because I would lost some essential information.
>
>    short res= clamp(short(v), lo,hi);  // not the expected
>                                        // behavior

That's the caller's fault, of course.

> That means that I will need to convert to the
>
>    short res= short(clamp(v, int(lo),int(hi)));

Right, but all of the information is visible to the caller.

You could also do that like this:

   clamp<int>(v, lo, hi)

For comparison with v, lo and hi must be promoted anyway, so the three-type version doesn't help.  Forcing the caller to disambiguate isn't so bad, at least in this case.

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer                     using std::disclaimer;
Dev Tools & Components
Susquehanna International Group, LLP  http://www.sig.com

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