Re: [boost] [ICL] some improvement proposals. Making selectors return const reference

Subject: Re: [boost] [ICL] some improvement proposals. Making selectors return const reference
From: Denis (comp.lib.boost.devel_at_[hidden])
Date: 2011-05-23 09:50:06

Hi

Another option could be to expose _lwr and _upr as public members of
interval (modelling after std::pair's `first` and `second`).

On Mon, May 23, 2011 at 1:16 PM, Joachim Faulhaber <afojgo_at_[hidden]>wrote:

> Hi Denis, list,
>
> thanks for your interest in Boost.ICL and for your input.
>
> First a side note on the subject line:
> You did what is stated in the boost discussion policy
> http://www.boost.org/community/policy.html
> which says:
> Put the Library Name in the Subject Line
> [ICL] some improvement proposals.
>
> Actually as you can see on the list the convention that is actually
> established is
>
> [boost][Libraryname] bla bla
>
> for the developers list and
>
> [Boost-users][Libraryname] bla bla
>
> for the user's list.
>
> *Would someone update the web page accordingly?*
>
> Next I'd like to refer to a suggestion you've sent in off-list:
>
> 2011/5/16 Denis <denis_at_[hidden]>:
> > Hi Joachim
> >
> > I also think that the functions upper() lower() first() last() have to
> > return const reference to domain_type instead of domain_type.
> > It is the same for int/double/time but has sense for my blobs.
> > Returning domain_type implies copying.
> > Same logic as std::vector's at().
>
> This is interesting.
>
> With first() and last(), I don't think it is possible, because,
> dependent on the type of interval, we may generate a local temporary
> object via increment (++) or decrement (--), which can not be referred
> to.
>
> On the contrary for upper() and lower(), we should always be able to
> pass the constant reference of the member variables of the interval as
> return value. As you say, this avoids copying operations that might
> decrease efficiency, if domain_type objects are large.
>
> I think a modification to the code can be done without breaking
> existing code, at least I hope so. We could use
>
> typedef boost::call_traits<domain_type>::param domain_return_type
>
> as return type of lower() and upper(), so pass by value can be kept
> for built in types.
>
> Still I am kind of reluctant when I think of implementing this
> optimization:
>
> (1) Return by value works well and fast for the majority of
> applications where domain_type is built-in or small
> (2) Return by value allows for compiler optimizations that are taking
> care for copy elision in many cases.
> (3) It would be nicer if all selectors had the same signatures
> (simplicity).
> (4) Customization of intervals will become more obscure, less
> understandable by the new domain_return_type.
> (5) We'd increase expert-friendliness for a concern that is relatively
> local:
>
> Using ICL::intervals and interval_containers with large domain objects
> is unfavorable anyway. If efficiency is a mayor issue, we would have
> to consider not using the large objects directly in intervals but
> introducing a level of indirection. We may refer to them through
> (smart)pointers or iterators which are small and use an induced
> ordering for the interval containers for the Compare template
> parameter.
>
> x < y <=> (*x) < (*y)
>
> So I'm not shure what to do. Currently I tend to consider an
> implementation of the proposal.
>
> Thoughts?
>
> Joachim
>
>
> --
> Interval Container Library [Boost.Icl]
> http://www.joachim-faulhaber.de
>