Re: [boost] set arithmetic proposal

From: Victor A. Wagner Jr. (vawjr_at_[hidden])
Date: 2005-06-02 08:25:58

At 16:16 2005-05-26, Dominic Herity wrote:
>I've often wished that STL sets supported set arithmetic operations.
>Addition, multiplication and subtraction operators could be overloaded with
>set union, intersection and difference respectively.
>
>For example:
>             set<char> s1;            // s1 <- {}
>             s1 += 'a';               // s1 <- {a}
>             set<char> s2 = s1 + 'b'; // s2 <- {a,b}
>             set<char> s3 = s2 - s1;  // s3 <- {b}
>             set<char> s4 = s1 * s2;  // s4 <- {a}
>
>Achieving the above results with the existing STL library is by comparison
>cumbersome, error-prone and unclear.
>
>Although this proposal does not follow the STL design philosophy, it meets a
>real developer need. It can be implemented using global operator overloads,
>which should avoid conflicts with other uses of STL sets.
>
>Comments and suggestions welcome.

I guess you and I must be the only two former Pascal programmers hanging 
around boost.  It seems to me that  "set of" from Pascal wasn't ever 
popular with anyone but those who really _really_ used them heavily (e.g. 
Ada dropped them when it was derived from Pascal).  I argued 
(unsuccessfully) that when the boost::dynamic_bitset<> was proposed that 
the _least_ we could do would be to fix the mis-characterization of 
operators <= and >= with regards to sets (for those who haven't studied 
sets,    {b,c,d} <= {a,b,c,d}  but that's not how it will evaluate with 
either std::set or boost::dynamic_bitset).  Absent that oddity, I suspect 
that you could rather easily overload some global operators to handle what 
you want using any of std::set, std::bitset, or boost::dynamic_bitset (the 
backwardness of the comparison operators would still bother me, 
though).  Hmmmm, maybe I should look more closely at the "unordered 
collections" (hash_set) proposal further and see if that correctly manages 
the set concept.

>Best Regards
>Dominic Herity
>Red Plain Technology (www.redplain.com)
>T:[phone] F: [phone] E: dominic.herity_at_[hidden]
>
>
>
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Victor A. Wagner Jr.      http://rudbek.com
The five most dangerous words in the English language:
               "There oughta be a law"