Re: Proposal: More flexible comparisons

From:
Victor Bazarov <v.Abazarov@comAcast.net>
Newsgroups:
comp.lang.c++
Date:
Thu, 25 Jun 2009 11:33:33 -0400
Message-ID:
<h205af$82e$1@news.datemas.de>
Jonathan Lee wrote:

I think the following simple approach will provide great flexibility in conditions.
...
if(1<x<4)


While we're on the topic, I wish there was an "in" operator, $B":(B. As in
set-theory membership. Then you might be able to write something like

if (x $B":(B (1,4)) { } // if (x in (1,4)) { }

Also while we're at it, unions, intersections, subset,...

No joke. That would be awesome.

--Jonathan


But you can do it yourself. You can define a class Interval with a
consturctor that takes two ends (or four classes: OpenInterval,
ClosedInterval, OpenClosedInterval, ClosedOpenInterval), and then define
an operator, say, equality. Here is pseudo code:

   template<class value_type> struct Interval_t
   {
       value_type from, to;

       Interval_t(value_type f, value_type t) : from(f), to(t) {}
   };

   template<class T> Interval_t<T> Interval(T f, T t)
   {
       return Interval_t<T>(f, t);
   }

   template<class T> bool operator ^ (T t, Interval_t<T> const& i)
   {
       return t > i.from && t < i.to;
   }

   int main()
   {
      bool in = 4 ^ Interval(1, 10));
      bout out = 444 ^ Interval(1, 10));
   }

V
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