From ad803b82b586d28bac10077a36f3cb4858ecbc68 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mael=20Rouxel-Labb=C3=A9?=
 <mael.rouxel.labbe@geometryfactory.com>
Date: Sun, 21 Jun 2020 12:03:53 +0200
Subject: [PATCH] Enhance is_convertible.h with boost::mpl rather than handmade
 enum { value = }

---
 STL_Extension/include/CGAL/is_iterator.h | 84 ++++++++++++++----------
 1 file changed, 48 insertions(+), 36 deletions(-)

diff --git a/STL_Extension/include/CGAL/is_iterator.h b/STL_Extension/include/CGAL/is_iterator.h
index 1e563aaf781..c6d25858a01 100644
--- a/STL_Extension/include/CGAL/is_iterator.h
+++ b/STL_Extension/include/CGAL/is_iterator.h
@@ -17,12 +17,14 @@
 #ifndef CGAL_IS_ITERATOR_H
 #define CGAL_IS_ITERATOR_H
 
-#include <iterator>
 #include <boost/type_traits/is_convertible.hpp>
 #include <boost/type_traits/is_pointer.hpp>
 #include <boost/type_traits/remove_reference.hpp>
 #include <boost/type_traits/remove_cv.hpp>
 #include <boost/mpl/has_xxx.hpp>
+#include <boost/mpl/logical.hpp>
+
+#include <iterator>
 
 namespace CGAL {
 namespace internal {
@@ -35,42 +37,52 @@ BOOST_MPL_HAS_XXX_TRAIT_DEF(reference)
 
 //We request the type to be either a pointer or to
 //provide all 5 nested types provided by iterator_traits
-template <class T> struct is_iterator_ {
-        enum { value =
-          ( has_iterator_category<T>::value &&
-            has_value_type<T>::value &&
-            has_difference_type<T>::value &&
-            has_pointer<T>::value &&
-            has_reference<T>::value
-          )
-                       || boost::is_pointer<T>::value };
-};
-
-template <class T,class U,bool=is_iterator_<T>::value>
-struct is_iterator_type_ {
-        enum { value=false };
-};
-template <class T,class U> struct is_iterator_type_<T,U,true> :
-        //boost::is_base_of<U,typename std::iterator_traits<T>::iterator_category>
-        boost::is_convertible<typename std::iterator_traits<T>::iterator_category,U>
-        {};
-
-}
-
-// NOTE: we don't want the real std::decay or functions are included
-template <class T> struct is_iterator :
-        internal::is_iterator_<typename boost::remove_cv<typename boost::remove_reference<T>::type>::type> {};
-
-template <class T,class Tag> struct is_iterator_type :
-        internal::is_iterator_type_<typename boost::remove_cv<typename boost::remove_reference<T>::type>::type,Tag> {};
-
-template <class T,class U,bool=is_iterator<T>::value> struct is_iterator_to {
-          enum { value=false };
-};
-template <class T,class U> struct is_iterator_to<T,U,true> :
-        boost::is_convertible<typename std::iterator_traits<T>::value_type,U>
+template <class T>
+struct is_iterator_
+  : public boost::mpl::or_<
+             boost::mpl::and_<
+               has_iterator_category<T>,
+               has_value_type<T>,
+               has_difference_type<T>,
+               has_pointer<T>,
+               has_reference<T> >,
+             boost::is_pointer<T> >
 { };
 
-}
+template <class T, class U, bool = is_iterator_<T>::value>
+struct is_iterator_type_
+  : public boost::mpl::false_
+{ };
+
+template <class T,class U>
+struct is_iterator_type_<T, U, true>
+  : public //boost::is_base_of<U,typename std::iterator_traits<T>::iterator_category>
+           boost::is_convertible<typename std::iterator_traits<T>::iterator_category, U>
+{ };
+
+} // namespace internal
+
+// NOTE: we don't want the real std::decay or functions are included
+template <class T>
+struct is_iterator
+  : public internal::is_iterator_<typename boost::remove_cv<typename boost::remove_reference<T>::type>::type>
+{ };
+
+template <class T, class Tag>
+struct is_iterator_type
+  : public internal::is_iterator_type_<typename boost::remove_cv<typename boost::remove_reference<T>::type>::type, Tag>
+{ };
+
+template <class T, class U, bool = is_iterator<T>::value>
+struct is_iterator_to
+  : public boost::mpl::false_
+{ };
+
+template <class T, class U>
+struct is_iterator_to<T, U, true>
+  : public boost::is_convertible<typename std::iterator_traits<T>::value_type, U>
+{ };
+
+} // namespace CGAL
 
 #endif // CGAL_IS_ITERATOR_H