Extended next/prior using patch from Daniel Walker (Daniel.Walker-at-bowneglobal.com)

[SVN r21382]

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

test/Jamfile

@@ -16,25 +16,28 @@ import testing ;
 # Make tests run by default.
 DEPENDS all : test ;
 
+local test_monitor = <lib>@boost/libs/test/build/boost_test_exec_monitor ;
+
 test-suite utility
     : 
         [ run ../iterator_traits_test.cpp ]
-        [ run ../iterators_test.cpp <lib>../../test/build/boost_test_exec_monitor ]
+        [ run ../iterators_test.cpp $(test_monitor) ]
         [ compile-fail ../noncopyable_test.cpp ]
         [ run ../numeric_traits_test.cpp ]
-        [ run ../operators_test.cpp <lib>../../test/build/boost_test_exec_monitor ]
-        [ run ../binary_search_test.cpp <lib>../../test/build/boost_test_exec_monitor ]
+        [ run ../operators_test.cpp $(test_monitor) ]
+        [ run ../binary_search_test.cpp $(test_monitor) ]
         [ run ../call_traits_test.cpp : -u ]
         [ compile-fail ../checked_delete_test.cpp ]
-        [ run ../compressed_pair_test.cpp <lib>../../test/build/boost_test_exec_monitor : -u ]
-        [ run ../addressof_test.cpp <lib>../../test/build/boost_test_exec_monitor ]
-        [ run ../ref_test.cpp <lib>../../test/build/boost_test_exec_monitor ]
-        [ run ../enable_if_constructors.cpp <lib>../../test/build/boost_test_exec_monitor ]
-        [ run ../enable_if_dummy_arg_disambiguation.cpp <lib>../../test/build/boost_test_exec_monitor ]
-        [ run ../enable_if_lazy.cpp <lib>../../test/build/boost_test_exec_monitor ]
-        [ run ../enable_if_lazy_test.cpp <lib>../../test/build/boost_test_exec_monitor ]
-        [ run ../enable_if_member_templates.cpp <lib>../../test/build/boost_test_exec_monitor ]
-        [ run ../enable_if_namespace_disambiguation.cpp <lib>../../test/build/boost_test_exec_monitor ]
-        [ run ../enable_if_no_disambiguation.cpp <lib>../../test/build/boost_test_exec_monitor ]
-        [ run ../enable_if_partial_specializations.cpp <lib>../../test/build/boost_test_exec_monitor ]
+        [ run ../compressed_pair_test.cpp $(test_monitor) : -u ]
+        [ run ../addressof_test.cpp $(test_monitor) ]
+        [ run ../ref_test.cpp $(test_monitor) ]
+        [ run ../enable_if_constructors.cpp $(test_monitor) ]
+        [ run ../enable_if_dummy_arg_disambiguation.cpp $(test_monitor) ]
+        [ run ../enable_if_lazy.cpp $(test_monitor) ]
+        [ run ../enable_if_lazy_test.cpp $(test_monitor) ]
+        [ run ../enable_if_member_templates.cpp $(test_monitor) ]
+        [ run ../enable_if_namespace_disambiguation.cpp $(test_monitor) ]
+        [ run ../enable_if_no_disambiguation.cpp $(test_monitor) ]
+        [ run ../enable_if_partial_specializations.cpp $(test_monitor) ]
+        [ run ../next_prior_test.cpp $(test_monitor) ]          
     ;

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;
+}

utility.htm

@@ -40,15 +40,33 @@
 			<pre>template &lt;class T&gt;
 T next(T x) { return ++x; }
 
-template &lt;class X&gt;
-T prior(T x) { return --x; }</pre>
+template &lt;class T, class Distance&gt;
+T next(T x, Distance n)
+{
+    std::advance(x, n);
+    return x;
+}
+
+template &lt;class T&gt;
+T prior(T x) { return --x; }
+
+template &lt;class T, class Distance&gt;
+T prior(T x, Distance n)
+{
+    std::advance(x, -n);
+    return x;
+}</pre>
 		</blockquote>
 		<p>Usage is simple:</p>
 		<blockquote>
 			<pre>const std::list&lt;T&gt;::iterator p = get_some_iterator();
-const std::list&lt;T&gt;::iterator prev = boost::prior(p);</pre>
+const std::list&lt;T&gt;::iterator prev = boost::prior(p);
+const std::list&lt;T&gt;::iterator next = boost::next(prev, 2);</pre>
 		</blockquote>
-		<p>Contributed by <a href="../../people/dave_abrahams.htm">Dave Abrahams</a>.</p>
+                <p>The distance from the given iterator should be supplied as an absolute value. For
+			example, the iterator four iterators prior to the given iterator <code>p</code>
+			may be obtained by <code>prior(p, 4)</code>.</p>
+		<p>Contributed by <a href="../../people/dave_abrahams.htm">Dave Abrahams</a>.  Two-argument versions by Daniel Walker.</p>
 		<h2><a name="Class_noncopyable">Class noncopyable</a></h2>
 		<p>Class <strong>noncopyable</strong> is a base class.&nbsp; Derive your own class 
 			from <strong>noncopyable</strong> when you want to prohibit copy construction 
@@ -122,7 +140,7 @@ void f() {
 		<p>See <a href="base_from_member.html">separate documentation</a>.</p>
 		<hr>
 		<p>Revised&nbsp; <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan
--->01 September, 2003<!--webbot bot="Timestamp" endspan i-checksum="38582"
+-->23 December, 2003<!--webbot bot="Timestamp" endspan i-checksum="38582"
 -->
 		</p>
 		<p>&copy; Copyright boost.org 1999-2003. Permission to copy, use, modify, sell and distribute