poll for properties

[Sean Kelly]

== Quote from Andrei Alexandrescu (SeeWebsiteForEmail at erdani.org)'s article
> Michel Fortin wrote:
> > On 2009-07-28 19:59:30 -0400, Andrei Alexandrescu
> > <SeeWebsiteForEmail at erdani.org> said:
> >
> >> The way Phobos does things is the following:
> >>
> >> a) You must define .empty which completes in O(1).
> >>
> >> b) If you can define .length with O(1), define it, otherwise don't.
> >>
> >> Then Phobos defines walkLength() on a best-effort basis which is
> >> guaranteed to finish in O(n) but may finish faster. It uses .length if
> >> defined, or else it just iterates the range to exhaustion.
> >
> > This looks like a good approach. I'm just not too thrilled by the name
> > "walkLength". But perhaps I'm the only one.
> STL defines distance() but people tend to forget it's O(n). So I chose a
> name that makes it rather obvious it's O(n).

To be fair, distance is as fast as the iterator allows.  If you pass a random
access iterator it's O(1).