Re: [boost] [dynamic_bitset] Comparison operators without assertions

On 5/11/2017 1:34 AM, degski via Boost wrote:

On 11 May 2017 at 08:11, Edward Diener via Boost wrote:

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There is no reason to change the right-to-left order as the most significant bit is on the right.

A bitset is not a number, 'most signifcant' depends on usage and is in the eye of the beholder.

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Furthermore it would be foolish to break backward compatibility on a whim.

Yes.

I will probably keep the same order but just add that the longer size, the

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rest being equal, will always be considered greater than the shorter size.

One could introduce a comparison-policy, the default preserving the 'current' behaviour.

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The only other possibility that I can imagine, if the assert is eliminated, is to throw some exception if the sizes are not equal, which at least has the possibility of keeping the program running if the exception is caught.

An exception seems completely wrong to me, as there is a valid use case for comparing bitsets of differing lengths. Exceptions should be used for exceptional situations, i.e. not here.

What I have ended up doing is to keep the exact same behavior as before when the bitsets are of equal size. When the bitsets are of unequal size, if either size is 0 that bitset is less than the other one. If neither size is 0 I convert both bitsets to an unsigned long using the already provided member function to_ulong() and use those values for the comparison. I have tested this out adding some tests for different sized bitsets. I have not pushed this to 'develop' yet. I wanted to post here my solution and then others could chime in if they wished. I found that it was completely wrong to do bit-by-bit comparisons when the bitsets were not the same size. No matter how I decided to do it the result was never correct. If anyone doubts this they can try it for themselves.

degski