From a4bacb5077662b04525e11d5ee67f970375046f4 Mon Sep 17 00:00:00 2001
From: Dave Abrahams <dave@boostpro.com>
Date: Tue, 23 Dec 2003 14:59:59 +0000
Subject: [PATCH] Extended next/prior using patch from Daniel Walker
 (Daniel.Walker-at-bowneglobal.com)

[SVN r21382]
---
 include/boost/next_prior.hpp | 20 +++++++++
 test/next_prior_test.cpp     | 79 ++++++++++++++++++++++++++++++++++++
 2 files changed, 99 insertions(+)
 create mode 100755 test/next_prior_test.cpp

diff --git a/include/boost/next_prior.hpp b/include/boost/next_prior.hpp
index d236766..3afeb78 100644
--- a/include/boost/next_prior.hpp
+++ b/include/boost/next_prior.hpp
@@ -8,9 +8,14 @@
 
 //  See http://www.boost.org/libs/utility for documentation.
 
+//  Revision History
+//  13 Dec 2003  Added next(x, n) and prior(x, n) (Daniel Walker)
+
 #ifndef BOOST_NEXT_PRIOR_HPP_INCLUDED
 #define BOOST_NEXT_PRIOR_HPP_INCLUDED
 
+#include <iterator>
+
 namespace boost {
 
 //  Helper functions for classes like bidirectional iterators not supporting
@@ -19,15 +24,30 @@ namespace boost {
 //  Usage:
 //    const std::list<T>::iterator p = get_some_iterator();
 //    const std::list<T>::iterator prev = boost::prior(p);
+//    const std::list<T>::iterator next = boost::next(prev, 2);
 
 //  Contributed by Dave Abrahams
 
 template <class T>
 inline T next(T x) { return ++x; }
 
+template <class T, class Distance>
+inline T next(T x, Distance n)
+{
+    std::advance(x, n);
+    return x;
+}
+
 template <class T>
 inline T prior(T x) { return --x; }
 
+template <class T, class Distance>
+inline T prior(T x, Distance n)
+{
+    std::advance(x, -n);
+    return x;
+}
+
 } // namespace boost
 
 #endif  // BOOST_NEXT_PRIOR_HPP_INCLUDED
diff --git a/test/next_prior_test.cpp b/test/next_prior_test.cpp
new file mode 100755
index 0000000..ebce472
--- /dev/null
+++ b/test/next_prior_test.cpp
@@ -0,0 +1,79 @@
+// Boost test program for next() and prior() utilities.
+
+// Copyright 2003 Daniel Walker.  Use, modification, and distribution
+// are subject to the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or a copy at
+// http://www.boost.org/LICENSE_1_0.txt.)
+
+// See http://www.boost.org/libs/utility for documentation.
+
+// Revision History 13 Dec 2003 Initial Version (Daniel Walker)
+
+// next() and prior() are replacements for operator+ and operator- for
+// non-random-access iterators. The semantics of these operators are
+// such that after executing j = i + n, std::distance(i, j) equals
+// n. Tests are provided to ensure next() has the same
+// result. Parallel tests are provided for prior(). The tests call
+// next() and prior() several times. next() and prior() are very
+// simple functions, though, and it would be very strange if these
+// tests were to fail.
+
+#define BOOST_INCLUDE_MAIN
+#include <boost/test/test_tools.hpp>
+
+#include <list>
+#include <vector>
+
+#include <boost/next_prior.hpp>
+
+template<class RandomAccessIterator, class ForwardIterator>
+bool plus_one_test(RandomAccessIterator first, RandomAccessIterator last, ForwardIterator first2)
+{
+    RandomAccessIterator i = first;
+    ForwardIterator j = first2;
+    while(i != last)
+        i = i + 1, j = boost::next(j);
+    return std::distance(first, i) == std::distance(first2, j);
+}
+
+template<class RandomAccessIterator, class ForwardIterator>
+bool plus_n_test(RandomAccessIterator first, RandomAccessIterator last, ForwardIterator first2)
+{
+    RandomAccessIterator i = first;
+    ForwardIterator j = first2;
+    for(int n = 0; i != last; ++n)
+        i = first + n, j = boost::next(first2, n);
+    return std::distance(first, i) == std::distance(first2, j);
+}
+
+template<class RandomAccessIterator, class BidirectionalIterator>
+bool minus_one_test(RandomAccessIterator first, RandomAccessIterator last, BidirectionalIterator last2)
+{
+    RandomAccessIterator i = last;
+    BidirectionalIterator j = last2;
+    while(i != first)
+        i = i - 1, j = boost::prior(j);
+    return std::distance(i, last) == std::distance(j, last2);
+}
+
+template<class RandomAccessIterator, class BidirectionalIterator>
+bool minus_n_test(RandomAccessIterator first, RandomAccessIterator last, BidirectionalIterator last2)
+{
+    RandomAccessIterator i = last;
+    BidirectionalIterator j = last2;
+    for(int n = 0; i != first; ++n)
+        i = last - n, j = boost::prior(last2, n);
+    return std::distance(i, last) == std::distance(j, last2);
+}
+
+int test_main(int, char*[])
+{
+    std::vector<int> x(8);
+    std::list<int> y(x.begin(), x.end());
+
+    BOOST_REQUIRE(plus_one_test(x.begin(), x.end(), y.begin()));
+    BOOST_REQUIRE(plus_n_test(x.begin(), x.end(), y.begin()));
+    BOOST_REQUIRE(minus_one_test(x.begin(), x.end(), y.end()));
+    BOOST_REQUIRE(minus_n_test(x.begin(), x.end(), y.end()));
+    return 0;
+}