Hi John, 2010/3/4 John Reid <j.reid@mail.cryst.bbk.ac.uk>:
Joachim Faulhaber wrote:
There has been a discussion on this point already. http://permalink.gmane.org/gmane.comp.lib.boost.devel/199905
For continuous data types it seems like interval bounds are needed as data member. For intervals of integral types the bound_type can be a static property. I will adapt the design in this point.
I assume most uses of the library will either be over discrete domains or continuous domains where the presence/absence of individual elements is irrelevant. In both cases right-open intervals are a natural way of implementing a solution. I haven't thought of an application over a continuous domain where it is necessary to cater for the inclusion/exclusion of individual elements. Do you know of one?
Personally, I haven't seen one. But the design of the ITL is based on the premise that interval sets/maps are sets/maps of elements. I have called this the fundamental view. Within this design it must always be possible to add or subtract individual elements or element value pairs to and from interval_sets/maps for all possible domain types. Given this premise, I need to provide a correct implementation for e.g. a subtraction of an element for continuous domain_types. Using open interval bounds this implementation can be given. I'm not aware of a good alternative.
So it might be better to have both continuous and discrete intervals as right-open by default and to allow some mechanism whereby the user can choose to allow different runtime bound types if they need them.
I agree, that right-open intervals are suitable as default. But I am afraid, for the continuous case, we can not guarantee that all operations can maintain such an invariant. BTW existing interval libraries e.g. boost::numeric::interval or FILIB++ work with closed intervals. Subtract a closed interval from an interval set with continuous domain_type and you need open bounds.
I have some further unrelated design questions/points:
Is there a function to return the distance between two intervals?
hull(x,y).left_subtract(x).right_subtract(y).length(); I admit this is not extremely elegant... I deliberately left functions and calculations out, that rely on distance measures, because, in the general case ITL intervals and interval containers only require an ordered domain type. So you can use strings, sequences or other data types that do not implement a distance measure.
The default interval type is closed. Isn't right-open a more natural choice for most applications?
Good question ... I tried to change this in the past but encountered problems with unsigned integral domain types that flipped to max_int by singular applications of decrement operator -- in the current implementation. May be I should check this point more thoroughly again. I could get rid of the unloved unon<T>() meta function. ...
It makes interval subtraction slightly simpler for example. I've always found right-open intervals an easier concept to think about and they make coding easier although this library removes any concerns about the latter.
What is the meaning of the cardinality of a continuous interval? It seems to be defined to be 0? Why not make it only available for discrete domains?
Try this: interval<double> x(0.0, 1.0); if(x.cardinality() == numeric_limits<interval<double>::size_type>::infinity()) cout << "cardinality is infinite\n"; for doubles a, b with a < b: [a,b).cardinality() == infinity but {[a,a],[b,b]}.cardinality() == 2 Function cardinality() has been introduced to make clear: This function yields the number of *elements*, and not the number of iteratable entities in the interval container. For continuous domain_types the cardinality of an interval container can be infinite but it can be finite as well.
I would like to see interoperability with other boost libraries such as boost.hash and boost.serialization. Both would be very useful for my current application.
I haven't checked this yet. There should be some kind of basic interoperability through (segment) iterators and element_iterators.
Why were the interval combining styles implemented as subclasses? Wouldn't the design have been more flexible if they were implemented as a policy template parameter? That's just my feeling about it, I don't feel qualified to offer a strong opinion.
Part of these things have an "historical" background. The lib started with an OO design in a commercial company and has seen a lot of refactorings, that tried to keep a kind of back compatibility.
- What is your evaluation of the documentation?
Good. A tutorial would be a welcome addition. Some functions were undocumented, I'm assuming they're documented in the review version.
The "handcrafted" documentation relates to the major interface of overloaded functions and function templates. In order to keep that short, more specific functions are only documented in the part of the documentation that is generated from doxygen comments:
http://www.joachim-faulhaber.de/boost_itl/doc/libs/itl/doc/html/interval_tem...
And yes, there may be few that have been forgotten. Please tell me, which ones you missed specifically.
I'll try to find them again.
Thanks and best regards, Joachim