cleanup in CGAL/Iterator_range.h

... and add a default constructor to create an
empty range (with singular iterators).

STL_Extension/include/CGAL/Iterator_range.h

@@ -18,56 +18,36 @@
 
 namespace CGAL {
 
-  /*!
-\ingroup PkgSTLExtensionRef
-  /// `CGAL::Iterator_range` is a...
-  */
-  template <typename I>
-  class Iterator_range
-    : public std::pair<I,I>{
-
-    typedef std::pair<I,I> Base;
-
-  public:
+/*!
+  \ingroup PkgSTLExtensionRef
+  `CGAL::Iterator_range` encapsulates two iterators so they fulfill the `ForwardRange` concept.
+  The class is essentially a clone of <A
+  href="https://www.boost.org/doc/libs/1_55_0/libs/range/doc/html/range/reference/utilities/iterator_range.html">`boost::iterator_range`</A>,
+  and it additionally is derived from `std::pair`, so that one can apply `boost::tie`.
+*/
+template <typename I>
+class Iterator_range : public std::pair<I, I>
+{
+  typedef std::pair<I, I> Base;
 
+public:
   typedef I iterator;
   typedef I const_iterator;
 
+  Iterator_range() = default;
   Iterator_range(I b, I e)
-      : Base(b,e)
-    {}
+      : Base(b, e) {}
+  Iterator_range(const std::pair<I, I>& ip)
+      : Base(ip) {}
 
-
-    // Iterator_range(const Iterator_range& ip)
-    //   : Base(ip)
-    // {}
-
-    Iterator_range(const std::pair<I,I>& ip)
-      : Base(ip)
-    {}
-
-  I begin() const
-  {
-    return this->first;
-  }
-
-  I end() const
-  {
-    return this->second;
-  }
+  I begin() const { return this->first; }
+  I end() const { return this->second; }
 
   /// returns `std::distance(begin(), end())`
-  std::size_t
-  size() const
-  {
-    return static_cast<std::size_t>(std::distance(begin(), end()));
-  }
+  std::size_t size() const { return static_cast<std::size_t>(std::distance(begin(), end())); }
 
   /// returns `std::distance(begin(), end())==0`
-  bool empty() const
-  {
-    return begin()==end();
-  }
+  bool empty() const { return begin() == end(); }
 
   operator std::tuple<I&, I&>()
   {
@@ -87,37 +67,25 @@ namespace CGAL {
   }
 };
 
-  template <typename T>
-  Iterator_range<T>
-  make_range(const T& b, const T&e)
-  {
+template <typename T>
+Iterator_range<T>
+make_range(const T& b, const T&e)
+{
   return Iterator_range<T>(b,e);
-  }
+}
 
-  template <typename T>
-  Iterator_range<T>
-  make_range(const std::pair<T,T>& p)
-  {
+template <typename T>
+Iterator_range<T>
+make_range(const std::pair<T,T>& p)
+{
   return Iterator_range<T>(p.first,p.second);
-  }
+}
 
 
 } // namespace CGAL
 
-// At global scope...
-
+namespace boost::foreach {
   template<typename T>
-inline boost::mpl::true_ *
-  boost_foreach_is_lightweight_proxy( CGAL::Iterator_range<T> *&, boost::foreach::tag )
-{
-    return 0;
+  struct is_lightweight_proxy<CGAL::Iterator_range<T>> : boost::mpl::true_ {};
 }
-namespace boost { namespace foreach
-{
-    template<typename T>
-    struct is_lightweight_proxy< CGAL::Iterator_range<T> >
-      : mpl::true_
-    {
-    };
-}}
 #endif // CGAL_ITERATOR_RANGE_H