Re: [boost] [gacap]Is any interesting to "Generating All Combinations and Permutations"？

From: Hervé Brönnimann (hervebronnimann_at_[hidden])
Date: 2007-11-13 07:58:25

Ben:  Good, we have half the work agreed, then.  There is no way you  
will be able to make classes into a a standard, it is too heavy  
compared to a single free-standing function.  This is an extension,  
and not a very important one, so it stands best chance for  
standardization if it is lightweight, crisp, and still remains  
useful.  I also don't see what classes bring that is so much better  
than free functions.

And after thinking a bit, I came to the conclusion that providing the  
assignments from [first, last) to values in [first_value, last_value)  
for permutations with repetitions, and multiplicities for  
combinations with repetitions, was the best representation for the  
input/output.  The user can use those to actually produce the  
permutations and combinations, i.e. replacing the value (iterator or  
integral index) by their elements pointed to in some input sequence,  
or copying the elements with the appropriate multiplicity, but it  
does away with a lot of things and simplifies the functions while  
retaining the core functionality.  Doing otherwise would impose  
constraints such as CopyConstructible and Assignable for the elements  
of the combinations, sorted input range and EqualityComparable, etc.   
Not quite clear what you would do also with elements not present in  
some combination (multiplicity 0), but that would become present in  
the next combination. Etc.

Hope that helps. I'm committed now to reach the best state for this  
proposal, so don't be shy criticizing my proposal.  If I can't defend  
the arguments or you have a better position, I'll be very happy that  
we can improve on it!
--HB

Let me continue to improve the proposal, and provide examples.  I

On Nov 13, 2007, at 3:33 AM, Ben Bear wrote:

> 2007/11/13, Hervé Brönnimann <hervebronnimann_at_[hidden]>:
>> Ben: Before you do any substantial work, please check my proposal.  I
>> have tried to provide background / explanations, and a set of
>> coherent interfaces.  Please look at:
>>
>> http://photon.poly.edu/~hbr/boost/combinations.html
>>
>> The code in the .hpp (linked) is only temporary and not debugged.  I
>> am in the process of writing test cases.  I'm happy to send it to you
>> too...  Keep in mind it is work in progress.  I have a job and am
>> spending far too much time on this at the moment :)
>> --HB
>>
>> PS: I am not sure about the Incrementor/Decrementor interfaces,
>> unless I can come up with a convincing example where the underlying
>> type is not int and does not have operator++ and operator--,  but it
>> still makes sense to count with it...
>>
>
> I agree with the eight "Without repetition" functions.
>
> But the "With Repetition", I think that providing classes, such as
> class gacap::repeat_permutation, is better than functions.  I had not
> thought how to privide functions about repetition version.  It's new
> thing to me.
>
> I'll read this proposal.  It's a little long for me.
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