Re: [boost] Ranged type mini-library submission

From: Rob Stewart (stewart_at_[hidden])
Date: 2004-05-18 12:06:12

From: christopher diggins <cdiggins_at_[hidden]>
> From: "Rob Stewart" <stewart_at_[hidden]>
> > From: christopher diggins <cdiggins_at_[hidden]>
> > > From: "Rob Stewart" <stewart_at_[hidden]>
> > >
> > > > I don't understand mytype::get_constraints().max() to not always
> > > > be available.  If I wanted that information, I'd write that
> > > > expression (instead of mytype::max()) and then be surprised when
> > > > it didn't work.
> > >
> > > When working with any parameterized type, it is natural to expect the
> return
> > > value of some functions to be of a type equal to a parameter. It is not
> > > natural to expect that the existance of methods to be conditional on the
> > > parameter.
> >
> > It is natural to assume that a parameterizing type meets the
> > requirements of the template upon which it is used.  If those
> > include supplying min() and max() functions, then there's no
> > surprise if things break when the parameterizing type fails to
> > meet its obligation.
> 
> Supplying min() and max() is not an implicit requirement on a constraints
> policy. If you had bothered to look at the code at
> http://www.cdiggins.com/constrained_value.hpp before jumping in this
> conversation and expressing your opinions, then you might have realized
> that.

Pardon me for assuming that design discussions take place before
implementing code.  You have posted various snippets and were
discussing various things; I was working from that context.

> > > > It's simple enough to require that the template parameter supply
> > > > min() and max() so that derivation yields those functions in
> > > > mytype's interface.  Then, it's a moot point whether min() and
> > > > max() are part of a static or non-static interface for mytype.
> > >
> > > The constrained_value type allows constraints which have nothing to do
> with
> > > min() and max() so requiring it in the parameter seems arbitrary.
> >
> > I don't get it.  Among the constraints are the minimum and
> > maximum values the type may assume, right?  Why wouldn't min()
> > and max() be part of that interface?
> 
> Again, if you looked at the code posted: http://www.cdiggins.com/cv_test.cpp
> you would have realized that a constraint policy can represent things as
> diverse as modulo'ed integers or integers divisble by a given number.

Possibly, but you posted rapid fire changes before design
discussions subsided on various points, so I didn't feel the need
to repeatedly download and view the code.

> > The desire to "dumb down" the interface is good until it bumps
> > into other goals.  Balance is the key.  The question is what is
> > more obvious to end users.  I contend, with Jeff, that c_v.max()
> > is more obvious and sensible than
> > c_v_type::get_constraints().max().  That c_v.max() imposes a
> > requirements on the parameterizing type, and that the
> > parameterizing type is used as a base class, is not critical in
> > my mind. The important thing is to document the requirements on
> > the parameterizing type and on the constrained_value class
> > template itself.
> >
> > You might have mentioned it in one of your posts, but I didn't
> > see where the object returned by c_v_type::get_constraints()
> > would get its minimum and maximum values.  Of what type is that
> > object?  How was that type determined?  (Note: I haven't looked
> > at your code, just your posts.)  The answers to those questions
> > will be telling as to how much you've reduced what you perceive
> > to be cognitive complexity among the design alternatives.
> 
> I don't feel particularly inclined to respond to your questions or concerns
> until you invest at least the minimum of effort required to take a look at
> the code and read the other posts related to this topic.

Fine.  You can justify your belligerence all you like.  I thought
I made some cogent arguments, despite the possibility of being
slightly off course.  A simple course correction from you would
have sufficed.  Since you prefer to attack rather than engage me,
I'll leave the discussion to you and Jeff.

-- 
Rob Stewart                           stewart_at_[hidden]
Software Engineer                     http://www.sig.com
Susquehanna International Group, LLP  using std::disclaimer;