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-<title>C++ Type traits</title>
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-
-<h2 align="center">C++ Type traits</h2>
-<p align="center"><em>by John Maddock and Steve Cleary</em></p>
-<p align="center"><em>This is a draft of an article that will appear in a future
-issue of </em><a href="http://www.ddj.com"><em>Dr Dobb's Journal</em></a></p>
-<p>Generic programming (writing code which works with any data type meeting a
-set of requirements) has become the method of choice for providing reusable
-code. However, there are times in generic programming when &quot;generic&quot;
-just isn't good enough - sometimes the differences between types are too large
-for an efficient generic implementation. This is when the traits technique
-becomes important - by encapsulating those properties that need to be considered
-on a type by type basis inside a traits class, we can minimise the amount of
-code that has to differ from one type to another, and maximise the amount of
-generic code.</p>
-<p>Consider an example: when working with character strings, one common
-operation is to determine the length of a null terminated string. Clearly it's
-possible to write generic code that can do this, but it turns out that there are
-much more efficient methods available: for example, the C library functions <font size="2" face="Courier New">strlen</font>
-and <font size="2" face="Courier New">wcslen</font> are usually written in
-assembler, and with suitable hardware support can be considerably faster than a
-generic version written in C++. The authors of the C++ standard library realised
-this, and abstracted the properties of <font size="2" face="Courier New">char</font>
-and <font size="2" face="Courier New">wchar_t</font> into the class <font size="2" face="Courier New">char_traits</font>.
-Generic code that works with character strings can simply use <font size="2" face="Courier New">char_traits&lt;&gt;::length</font>
-to determine the length of a null terminated string, safe in the knowledge that
-specialisations of <font size="2" face="Courier New">char_traits</font> will use
-the most appropriate method available to them.</p>
-<h4>Type traits</h4>
-<p>Class <font size="2" face="Courier New">char_traits</font> is a classic
-example of a collection of type specific properties wrapped up in a single class
- what Nathan Myers termed a <i>baggage class</i>[1]. In the Boost type-traits
-library, we[2] have written a set of very specific traits classes, each of which
-encapsulate a single trait from the C++ type system; for example, is a type a
-pointer or a reference type? Or does a type have a trivial constructor, or a
-const-qualifier? The type-traits classes share a unified design: each class has
-a single member <i>value</i>, a compile-time constant that is true if the type
-has the specified property, and false otherwise. As we will show, these classes
-can be used in generic programming to determine the properties of a given type
-and introduce optimisations that are appropriate for that case.</p>
-<p>The type-traits library also contains a set of classes that perform a
-specific transformation on a type; for example, they can remove a top-level
-const or volatile qualifier from a type. Each class that performs a
-transformation defines a single typedef-member <i>type</i> that is the result of
-the transformation. All of the type-traits classes are defined inside namespace <font size="2" face="Courier New">boost</font>;
-for brevity, namespace-qualification is omitted in most of the code samples
-given.</p>
-<h4>Implementation</h4>
-<p>There are far too many separate classes contained in the type-traits library
-to give a full implementation here - see the source code in the Boost library
-for the full details - however, most of the implementation is fairly repetitive
-anyway, so here we will just give you a flavour for how some of the classes are
-implemented. Beginning with possibly the simplest class in the library, is_void&lt;T&gt;
-has a member <i>value</i> that is true only if T is void.</p>
-<pre>template &lt;typename T&gt; 
-struct is_void
-{ static const bool value = false; };
-
-template &lt;&gt; 
-struct is_void&lt;void&gt;
-{ static const bool value = true; };</pre>
-<p>Here we define a primary version of the template class <font size="2" face="Courier New">is_void</font>,
-and provide a full-specialisation when T is void. While full specialisation of a
-template class is an important technique, sometimes we need a solution that is
-halfway between a fully generic solution, and a full specialisation. This is
-exactly the situation for which the standards committee defined partial
-template-class specialisation. As an example, consider the class
-boost::is_pointer&lt;T&gt;: here we needed a primary version that handles all
-the cases where T is not a pointer, and a partial specialisation to handle all
-the cases where T is a pointer:</p>
-<pre>template &lt;typename T&gt; 
-struct is_pointer 
-{ static const bool value = false; };
-
-template &lt;typename T&gt; 
-struct is_pointer&lt;T*&gt; 
-{ static const bool value = true; };</pre>
-<p>The syntax for partial specialisation is somewhat arcane and could easily
-occupy an article in its own right; like full specialisation, in order to write
-a partial specialisation for a class, you must first declare the primary
-template. The partial specialisation contains an extra &lt;<EFBFBD>&gt; after the
-class name that contains the partial specialisation parameters; these define the
-types that will bind to that partial specialisation rather than the default
-template. The rules for what can appear in a partial specialisation are somewhat
-convoluted, but as a rule of thumb if you can legally write two function
-overloads of the form:</p>
-<pre>void foo(T);
-void foo(U);</pre>
-<p>Then you can also write a partial specialisation of the form:</p>
-<pre>template &lt;typename T&gt;
-class c{ /*details*/ };
-
-template &lt;typename T&gt;
-
-class c&lt;U&gt;{ /*details*/ };</pre>
-<p>This rule is by no means foolproof, but it is reasonably simple to remember
-and close enough to the actual rule to be useful for everyday use.</p>
-<p>As a more complex example of partial specialisation consider the class
-remove_bounds&lt;T&gt;. This class defines a single typedef-member <i>type</i>
-that is the same type as T but with any top-level array bounds removed; this is
-an example of a traits class that performs a transformation on a type:</p>
-<pre>template &lt;typename T&gt; 
-struct remove_bounds
-{ typedef T type; };
-
-template &lt;typename T, std::size_t N&gt; 
-struct remove_bounds&lt;T[N]&gt;
-{ typedef T type; };</pre>
-<p>The aim of remove_bounds is this: imagine a generic algorithm that is passed
-an array type as a template parameter, <font size="2" face="Courier New">remove_bounds</font>
-provides a means of determining the underlying type of the array. For example <code>remove_bounds&lt;int[4][5]&gt;::type</code>
-would evaluate to the type <code>int[5]</code>. This example also shows that the
-number of template parameters in a partial specialisation does not have to match
-the number in the default template. However, the number of parameters that
-appear after the class name do have to match the number and type of the
-parameters in the default template.</p>
-<h4>Optimised copy</h4>
-<p>As an example of how the type traits classes can be used, consider the
-standard library algorithm copy:</p>
-<pre>template&lt;typename Iter1, typename Iter2&gt;
-Iter2 copy(Iter1 first, Iter1 last, Iter2 out);</pre>
-<p>Obviously, there's no problem writing a generic version of copy that works
-for all iterator types Iter1 and Iter2; however, there are some circumstances
-when the copy operation can best be performed by a call to <font size="2" face="Courier New">memcpy</font>.
-In order to implement copy in terms of <font size="2" face="Courier New">memcpy</font>
-all of the following conditions need to be met:</p>
-<ul>
-  <li>Both of the iterator types Iter1 and Iter2 must be pointers.</li>
-  <li>Both Iter1 and Iter2 must point to the same type - excluding <font size="2" face="Courier New">const</font>
-    and <font size="2" face="Courier New">volatile</font>-qualifiers.</li>
-  <li>The type pointed to by Iter1 must have a trivial assignment operator.</li>
-</ul>
-<p>By trivial assignment operator we mean that the type is either a scalar
-type[3] or:</p>
-<ul>
-  <li>The type has no user defined assignment operator.</li>
-  <li>The type does not have any data members that are references.</li>
-  <li>All base classes, and all data member objects must have trivial assignment
-    operators.</li>
-</ul>
-<p>If all these conditions are met then a type can be copied using <font size="2" face="Courier New">memcpy</font>
-rather than using a compiler generated assignment operator. The type-traits
-library provides a class <i>has_trivial_assign</i>, such that <code>has_trivial_assign&lt;T&gt;::value</code>
-is true only if T has a trivial assignment operator. This class &quot;just
-works&quot; for scalar types, but has to be explicitly specialised for
-class/struct types that also happen to have a trivial assignment operator. In
-other words if <i>has_trivial_assign</i> gives the wrong answer, it will give
-the &quot;safe&quot; wrong answer - that trivial assignment is not allowable.</p>
-<p>The code for an optimised version of copy that uses <font size="2" face="Courier New">memcpy</font>
-where appropriate is given in listing 1. The code begins by defining a template
-class <i>copier</i>, that takes a single Boolean template parameter, and has a
-static template member function <font size="2" face="Courier New">do_copy</font>
-which performs the generic version of <font size="2">copy</font> (in other words
-the &quot;slow but safe version&quot;). Following that there is a specialisation
-for <i>copier&lt;true&gt;</i>: again this defines a static template member
-function <font size="2" face="Courier New">do_copy</font>, but this version uses
-memcpy to perform an &quot;optimised&quot; copy.</p>
-<p>In order to complete the implementation, what we need now is a version of
-copy, that calls <code>copier&lt;true&gt;::do_copy</code> if it is safe to use <font size="2" face="Courier New">memcpy</font>,
-and otherwise calls <code>copier&lt;false&gt;::do_copy</code> to do a
-&quot;generic&quot; copy. This is what the version in listing 1 does. To
-understand how the code works look at the code for <font size="2" face="Courier New">copy</font>
-and consider first the two typedefs <i>v1_t</i> and <i>v2_t</i>. These use <code>std::iterator_traits&lt;Iter1&gt;::value_type</code>
-to determine what type the two iterators point to, and then feed the result into
-another type-traits class <i>remove_cv</i> that removes the top-level
-const-volatile-qualifiers: this will allow copy to compare the two types without
-regard to const- or volatile-qualifiers. Next, <font size="2" face="Courier New">copy</font>
-declares an enumerated value <i>can_opt</i> that will become the template
-parameter to copier - declaring this here as a constant is really just a
-convenience - the value could be passed directly to class <font size="2" face="Courier New">copier</font>.
-The value of <i>can_opt</i> is computed by verifying that all of the following
-are true:</p>
-<ul>
-  <li>first that the two iterators point to the same type by using a type-traits
-    class <i>is_same</i>.</li>
-  <li>Then that both iterators are real pointers - using the class <i>is_pointer</i>
-    described above.</li>
-  <li>Finally that the pointed-to types have a trivial assignment operator using
-    <i>has_trivial_assign</i>.</li>
-</ul>
-<p>Finally we can use the value of <i>can_opt</i> as the template argument to
-copier - this version of copy will now adapt to whatever parameters are passed
-to it, if its possible to use <font size="2" face="Courier New">memcpy</font>,
-then it will do so, otherwise it will use a generic copy.</p>
-<h4>Was it worth it?</h4>
-<p>It has often been repeated in these columns that &quot;premature optimisation
-is the root of all evil&quot; [4]. So the question must be asked: was our
-optimisation premature? To put this in perspective the timings for our version
-of copy compared a conventional generic copy[5] are shown in table 1.</p>
-<p>Clearly the optimisation makes a difference in this case; but, to be fair,
-the timings are loaded to exclude cache miss effects - without this accurate
-comparison between algorithms becomes difficult. However, perhaps we can add a
-couple of caveats to the premature optimisation rule:</p>
-<ul>
-  <li>If you use the right algorithm for the job in the first place then
-    optimisation will not be required; in some cases, <font size="2" face="Courier New">memcpy</font>
-    is the right algorithm.</li>
-  <li>If a component is going to be reused in many places by many people then
-    optimisations may well be worthwhile where they would not be so for a single
-    case - in other words, the likelihood that the optimisation will be
-    absolutely necessary somewhere, sometime is that much higher. Just as
-    importantly the perceived value of the stock implementation will be higher:
-    there is no point standardising an algorithm if users reject it on the
-    grounds that there are better, more heavily optimised versions available.</li>
-</ul>
-<h4>Table 1: Time taken to copy 1000 elements using copy&lt;const T*, T*&gt;
-(times in micro-seconds)</h4>
-<table border="1" cellpadding="7" cellspacing="1" width="529">
-  <tr>
-    <td valign="top" width="33%">
-      <p align="center">Version</p>
-    </td>
-    <td valign="top" width="33%">
-      <p align="center">T</p>
-    </td>
-    <td valign="top" width="33%">
-      <p align="center">Time</p>
-    </td>
-  </tr>
-  <tr>
-    <td valign="top" width="33%">&quot;Optimised&quot; copy</td>
-    <td valign="top" width="33%">char</td>
-    <td valign="top" width="33%">0.99</td>
-  </tr>
-  <tr>
-    <td valign="top" width="33%">Conventional copy</td>
-    <td valign="top" width="33%">char</td>
-    <td valign="top" width="33%">8.07</td>
-  </tr>
-  <tr>
-    <td valign="top" width="33%">&quot;Optimised&quot; copy</td>
-    <td valign="top" width="33%">int</td>
-    <td valign="top" width="33%">2.52</td>
-  </tr>
-  <tr>
-    <td valign="top" width="33%">Conventional copy</td>
-    <td valign="top" width="33%">int</td>
-    <td valign="top" width="33%">8.02</td>
-  </tr>
-</table>
-<p>&nbsp;</p>
-<h4>Pair of References</h4>
-<p>The optimised copy example shows how type traits may be used to perform
-optimisation decisions at compile-time. Another important usage of type traits
-is to allow code to compile that otherwise would not do so unless excessive
-partial specialization is used. This is possible by delegating partial
-specialization to the type traits classes. Our example for this form of usage is
-a pair that can hold references [6].</p>
-<p>First, let us examine the definition of &quot;std::pair&quot;, omitting the
-comparision operators, default constructor, and template copy constructor for
-simplicity:</p>
-<pre>template &lt;typename T1, typename T2&gt; 
-struct pair 
-{
-  typedef T1 first_type;
-  typedef T2 second_type;
-
-  T1 first;
-  T2 second;
-
-  pair(const T1 &amp; nfirst, const T2 &amp; nsecond)
-  :first(nfirst), second(nsecond) { }
-};</pre>
-<p>Now, this &quot;pair&quot; cannot hold references as it currently stands,
-because the constructor would require taking a reference to a reference, which
-is currently illegal [7]. Let us consider what the constructor's parameters
-would have to be in order to allow &quot;pair&quot; to hold non-reference types,
-references, and constant references:</p>
-<table border="1" cellpadding="7" cellspacing="1" width="638">
-  <tr>
-    <td valign="top" width="50%">Type of &quot;T1&quot;</td>
-    <td valign="top" width="50%">Type of parameter to initializing constructor</td>
-  </tr>
-  <tr>
-    <td valign="top" width="50%">
-      <pre>T</pre>
-    </td>
-    <td valign="top" width="50%">
-      <pre>const T &amp;</pre>
-    </td>
-  </tr>
-  <tr>
-    <td valign="top" width="50%">
-      <pre>T &amp;</pre>
-    </td>
-    <td valign="top" width="50%">
-      <pre>T &amp;</pre>
-    </td>
-  </tr>
-  <tr>
-    <td valign="top" width="50%">
-      <pre>const T &amp;</pre>
-    </td>
-    <td valign="top" width="50%">
-      <pre>const T &amp;</pre>
-    </td>
-  </tr>
-</table>
-<p>A little familiarity with the type traits classes allows us to construct a
-single mapping that allows us to determine the type of parameter from the type
-of the contained class. The type traits classes provide a transformation &quot;add_reference&quot;,
-which adds a reference to its type, unless it is already a reference.</p>
-<table border="1" cellpadding="7" cellspacing="1" width="580">
-  <tr>
-    <td valign="top" width="21%">Type of &quot;T1&quot;</td>
-    <td valign="top" width="27%">Type of &quot;const T1&quot;</td>
-    <td valign="top" width="53%">Type of &quot;add_reference&lt;const
-      T1&gt;::type&quot;</td>
-  </tr>
-  <tr>
-    <td valign="top" width="21%">
-      <pre>T</pre>
-    </td>
-    <td valign="top" width="27%">
-      <pre>const T</pre>
-    </td>
-    <td valign="top" width="53%">
-      <pre>const T &amp;</pre>
-    </td>
-  </tr>
-  <tr>
-    <td valign="top" width="21%">
-      <pre>T &amp;</pre>
-    </td>
-    <td valign="top" width="27%">
-      <pre>T &amp; [8]</pre>
-    </td>
-    <td valign="top" width="53%">
-      <pre>T &amp;</pre>
-    </td>
-  </tr>
-  <tr>
-    <td valign="top" width="21%">
-      <pre>const T &amp;</pre>
-    </td>
-    <td valign="top" width="27%">
-      <pre>const T &amp;</pre>
-    </td>
-    <td valign="top" width="53%">
-      <pre>const T &amp;</pre>
-    </td>
-  </tr>
-</table>
-<p>This allows us to build a primary template definition for &quot;pair&quot;
-that can contain non-reference types, reference types, and constant reference
-types:</p>
-<pre>template &lt;typename T1, typename T2&gt; 
-struct pair 
-{
-  typedef T1 first_type;
-  typedef T2 second_type;
-
-  T1 first;
-  T2 second;
-
-  pair(boost::add_reference&lt;const T1&gt;::type nfirst,
-       boost::add_reference&lt;const T2&gt;::type nsecond)
-  :first(nfirst), second(nsecond) { }
-};</pre>
-<p>Add back in the standard comparision operators, default constructor, and
-template copy constructor (which are all the same), and you have a std::pair
-that can hold reference types!</p>
-<p>This same extension <i>could</i> have been done using partial template
-specialization of &quot;pair&quot;, but to specialize &quot;pair&quot; in this
-way would require three partial specializations, plus the primary template. Type
-traits allows us to define a single primary template that adjusts itself
-auto-magically to any of these partial specializations, instead of a brute-force
-partial specialization approach. Using type traits in this fashion allows
-programmers to delegate partial specialization to the type traits classes,
-resulting in code that is easier to maintain and easier to understand.</p>
-<h4>Conclusion</h4>
-<p>We hope that in this article we have been able to give you some idea of what
-type-traits are all about. A more complete listing of the available classes are
-in the boost documentation, along with further examples using type traits.
-Templates have enabled C++ uses to take the advantage of the code reuse that
-generic programming brings; hopefully this article has shown that generic
-programming does not have to sink to the lowest common denominator, and that
-templates can be optimal as well as generic.</p>
-<h4>Acknowledgements</h4>
-<p>The authors would like to thank Beman Dawes and Howard Hinnant for their
-helpful comments when preparing this article.</p>
-<h4>References</h4>
-<ol>
-  <li>Nathan C. Myers, C++ Report, June 1995.</li>
-  <li>The type traits library is based upon contributions by Steve Cleary, Beman
-    Dawes, Howard Hinnant and John Maddock: it can be found at www.boost.org.</li>
-  <li>A scalar type is an arithmetic type (i.e. a built-in integer or floating
-    point type), an enumeration type, a pointer, a pointer to member, or a
-    const- or volatile-qualified version of one of these types.</li>
-  <li>This quote is from Donald Knuth, ACM Computing Surveys, December 1974, pg
-    268.</li>
-  <li>The test code is available as part of the boost utility library (see
-    algo_opt_examples.cpp), the code was compiled with gcc 2.95 with all
-    optimisations turned on, tests were conducted on a 400MHz Pentium II machine
-    running Microsoft Windows 98.</li>
-  <li>John Maddock and Howard Hinnant have submitted a &quot;compressed_pair&quot;
-    library to Boost, which uses a technique similar to the one described here
-    to hold references. Their pair also uses type traits to determine if any of
-    the types are empty, and will derive instead of contain to conserve space --
-    hence the name &quot;compressed&quot;.</li>
-  <li>This is actually an issue with the C++ Core Language Working Group (issue
-    #106), submitted by Bjarne Stroustrup. The tentative resolution is to allow
-    a &quot;reference to a reference to T&quot; to mean the same thing as a
-    &quot;reference to T&quot;, but only in template instantiation, in a method
-    similar to multiple cv-qualifiers.</li>
-  <li>For those of you who are wondering why this shouldn't be const-qualified,
-    remember that references are always implicitly constant (for example, you
-    can't re-assign a reference). Remember also that &quot;const T &amp;&quot;
-    is something completely different. For this reason, cv-qualifiers on
-    template type arguments that are references are ignored.</li>
-</ol>
-<h2>Listing 1</h2>
-<pre>namespace detail{
-
-template &lt;bool b&gt;
-struct copier
-{
-   template&lt;typename I1, typename I2&gt;
-   static I2 do_copy(I1 first, 
-                     I1 last, I2 out);
-};
-
-template &lt;bool b&gt;
-template&lt;typename I1, typename I2&gt;
-I2 copier&lt;b&gt;::do_copy(I1 first, 
-                      I1 last, 
-                      I2 out)
-{
-   while(first != last)
-   {
-      *out = *first;
-      ++out;
-      ++first;
-   }
-   return out;
-}
-
-template &lt;&gt;
-struct copier&lt;true&gt;
-{
-   template&lt;typename I1, typename I2&gt;
-   static I2* do_copy(I1* first, I1* last, I2* out)
-   {
-      memcpy(out, first, (last-first)*sizeof(I2));
-      return out+(last-first);
-   }
-};
-
-}
-
-template&lt;typename I1, typename I2&gt;
-inline I2 copy(I1 first, I1 last, I2 out)
-{
-   typedef typename 
-    boost::remove_cv&lt;
-     typename std::iterator_traits&lt;I1&gt;
-      ::value_type&gt;::type v1_t;
-
-   typedef typename 
-    boost::remove_cv&lt;
-     typename std::iterator_traits&lt;I2&gt;
-      ::value_type&gt;::type v2_t;
-
-   enum{ can_opt = 
-      boost::is_same&lt;v1_t, v2_t&gt;::value
-      &amp;&amp; boost::is_pointer&lt;I1&gt;::value
-      &amp;&amp; boost::is_pointer&lt;I2&gt;::value
-      &amp;&amp; boost::
-      has_trivial_assign&lt;v1_t&gt;::value 
-   };
-
-   return detail::copier&lt;can_opt&gt;::
-      do_copy(first, last, out);
-}</pre>
-<hr>
-<p><EFBFBD> Copyright John Maddock and Steve Cleary, 2000</p>
-
-</body>
-
-</html>
--- a/include/boost/detail/call_traits.hpp
+++ b/include/boost/detail/call_traits.hpp
@@ -0,0 +1,155 @@
+//  (C) Copyright Steve Cleary, Beman Dawes, Howard Hinnant & John Maddock 2000.
+//  Use, modification and distribution are subject to the Boost Software License,
+//  Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt).
+//
+//  See http://www.boost.org/libs/utility for most recent version including documentation.
+
+// call_traits: defines typedefs for function usage
+// (see libs/utility/call_traits.htm)
+
+/* Release notes:
+   23rd July 2000:
+      Fixed array specialization. (JM)
+      Added Borland specific fixes for reference types
+      (issue raised by Steve Cleary).
+*/
+
+#ifndef BOOST_DETAIL_CALL_TRAITS_HPP
+#define BOOST_DETAIL_CALL_TRAITS_HPP
+
+#ifndef BOOST_CONFIG_HPP
+#include <boost/config.hpp>
+#endif
+#include <cstddef>
+
+#include <boost/type_traits/is_arithmetic.hpp>
+#include <boost/type_traits/is_pointer.hpp>
+#include <boost/detail/workaround.hpp>
+
+namespace boost{
+
+namespace detail{
+
+template <typename T, bool small_>
+struct ct_imp2
+{
+   typedef const T& param_type;
+};
+
+template <typename T>
+struct ct_imp2<T, true>
+{
+   typedef const T param_type;
+};
+
+template <typename T, bool isp, bool b1>
+struct ct_imp
+{
+   typedef const T& param_type;
+};
+
+template <typename T, bool isp>
+struct ct_imp<T, isp, true>
+{
+   typedef typename ct_imp2<T, sizeof(T) <= sizeof(void*)>::param_type param_type;
+};
+
+template <typename T, bool b1>
+struct ct_imp<T, true, b1>
+{
+   typedef T const param_type;
+};
+
+}
+
+template <typename T>
+struct call_traits
+{
+public:
+   typedef T value_type;
+   typedef T& reference;
+   typedef const T& const_reference;
+   //
+   // C++ Builder workaround: we should be able to define a compile time
+   // constant and pass that as a single template parameter to ct_imp<T,bool>,
+   // however compiler bugs prevent this - instead pass three bool's to
+   // ct_imp<T,bool,bool,bool> and add an extra partial specialisation
+   // of ct_imp to handle the logic. (JM)
+   typedef typename boost::detail::ct_imp<
+      T,
+      ::boost::is_pointer<T>::value,
+      ::boost::is_arithmetic<T>::value
+   >::param_type param_type;
+};
+
+template <typename T>
+struct call_traits<T&>
+{
+   typedef T& value_type;
+   typedef T& reference;
+   typedef const T& const_reference;
+   typedef T& param_type;  // hh removed const
+};
+
+#if BOOST_WORKAROUND( __BORLANDC__,  BOOST_TESTED_AT( 0x570 ) )
+// these are illegal specialisations; cv-qualifies applied to
+// references have no effect according to [8.3.2p1],
+// C++ Builder requires them though as it treats cv-qualified
+// references as distinct types...
+template <typename T>
+struct call_traits<T&const>
+{
+   typedef T& value_type;
+   typedef T& reference;
+   typedef const T& const_reference;
+   typedef T& param_type;  // hh removed const
+};
+template <typename T>
+struct call_traits<T&volatile>
+{
+   typedef T& value_type;
+   typedef T& reference;
+   typedef const T& const_reference;
+   typedef T& param_type;  // hh removed const
+};
+template <typename T>
+struct call_traits<T&const volatile>
+{
+   typedef T& value_type;
+   typedef T& reference;
+   typedef const T& const_reference;
+   typedef T& param_type;  // hh removed const
+};
+#endif
+#if !defined(BOOST_NO_ARRAY_TYPE_SPECIALIZATIONS)
+template <typename T, std::size_t N>
+struct call_traits<T [N]>
+{
+private:
+   typedef T array_type[N];
+public:
+   // degrades array to pointer:
+   typedef const T* value_type;
+   typedef array_type& reference;
+   typedef const array_type& const_reference;
+   typedef const T* const param_type;
+};
+
+template <typename T, std::size_t N>
+struct call_traits<const T [N]>
+{
+private:
+   typedef const T array_type[N];
+public:
+   // degrades array to pointer:
+   typedef const T* value_type;
+   typedef array_type& reference;
+   typedef const array_type& const_reference;
+   typedef const T* const param_type;
+};
+#endif
+
+}
+
+#endif // BOOST_DETAIL_CALL_TRAITS_HPP
--- a/include/boost/detail/compressed_pair.hpp
+++ b/include/boost/detail/compressed_pair.hpp
@@ -0,0 +1,432 @@
+//  (C) Copyright Steve Cleary, Beman Dawes, Howard Hinnant & John Maddock 2000.
+//  Use, modification and distribution are subject to the Boost Software License,
+//  Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt).
+//
+//  See http://www.boost.org/libs/utility for most recent version including documentation.
+
+// compressed_pair: pair that "compresses" empty members
+// (see libs/utility/compressed_pair.htm)
+//
+// JM changes 25 Jan 2004:
+// For the case where T1 == T2 and both are empty, then first() and second()
+// should return different objects.
+// JM changes 25 Jan 2000:
+// Removed default arguments from compressed_pair_switch to get
+// C++ Builder 4 to accept them
+// rewriten swap to get gcc and C++ builder to compile.
+// added partial specialisations for case T1 == T2 to avoid duplicate constructor defs.
+
+#ifndef BOOST_DETAIL_COMPRESSED_PAIR_HPP
+#define BOOST_DETAIL_COMPRESSED_PAIR_HPP
+
+#include <algorithm>
+
+#include <boost/type_traits/remove_cv.hpp>
+#include <boost/type_traits/is_empty.hpp>
+#include <boost/type_traits/is_same.hpp>
+#include <boost/call_traits.hpp>
+
+namespace boost
+{
+
+template <class T1, class T2>
+class compressed_pair;
+
+
+// compressed_pair
+
+namespace details
+{
+   // JM altered 26 Jan 2000:
+   template <class T1, class T2, bool IsSame, bool FirstEmpty, bool SecondEmpty>
+   struct compressed_pair_switch;
+
+   template <class T1, class T2>
+   struct compressed_pair_switch<T1, T2, false, false, false>
+      {static const int value = 0;};
+
+   template <class T1, class T2>
+   struct compressed_pair_switch<T1, T2, false, true, true>
+      {static const int value = 3;};
+
+   template <class T1, class T2>
+   struct compressed_pair_switch<T1, T2, false, true, false>
+      {static const int value = 1;};
+
+   template <class T1, class T2>
+   struct compressed_pair_switch<T1, T2, false, false, true>
+      {static const int value = 2;};
+
+   template <class T1, class T2>
+   struct compressed_pair_switch<T1, T2, true, true, true>
+      {static const int value = 4;};
+
+   template <class T1, class T2>
+   struct compressed_pair_switch<T1, T2, true, false, false>
+      {static const int value = 5;};
+
+   template <class T1, class T2, int Version> class compressed_pair_imp;
+
+#ifdef __GNUC__
+   // workaround for GCC (JM):
+   using std::swap;
+#endif
+   //
+   // can't call unqualified swap from within classname::swap
+   // as Koenig lookup rules will find only the classname::swap
+   // member function not the global declaration, so use cp_swap
+   // as a forwarding function (JM):
+   template <typename T>
+   inline void cp_swap(T& t1, T& t2)
+   {
+#ifndef __GNUC__
+      using std::swap;
+#endif
+      swap(t1, t2);
+   }
+
+   // 0    derive from neither
+
+   template <class T1, class T2>
+   class compressed_pair_imp<T1, T2, 0>
+   {
+   public:
+      typedef T1                                                 first_type;
+      typedef T2                                                 second_type;
+      typedef typename call_traits<first_type>::param_type       first_param_type;
+      typedef typename call_traits<second_type>::param_type      second_param_type;
+      typedef typename call_traits<first_type>::reference        first_reference;
+      typedef typename call_traits<second_type>::reference       second_reference;
+      typedef typename call_traits<first_type>::const_reference  first_const_reference;
+      typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+      compressed_pair_imp() {} 
+
+      compressed_pair_imp(first_param_type x, second_param_type y)
+         : first_(x), second_(y) {}
+
+      compressed_pair_imp(first_param_type x)
+         : first_(x) {}
+
+      compressed_pair_imp(second_param_type y)
+         : second_(y) {}
+
+      first_reference       first()       {return first_;}
+      first_const_reference first() const {return first_;}
+
+      second_reference       second()       {return second_;}
+      second_const_reference second() const {return second_;}
+
+      void swap(::boost::compressed_pair<T1, T2>& y)
+      {
+         cp_swap(first_, y.first());
+         cp_swap(second_, y.second());
+      }
+   private:
+      first_type first_;
+      second_type second_;
+   };
+
+   // 1    derive from T1
+
+   template <class T1, class T2>
+   class compressed_pair_imp<T1, T2, 1>
+      : private ::boost::remove_cv<T1>::type
+   {
+   public:
+      typedef T1                                                 first_type;
+      typedef T2                                                 second_type;
+      typedef typename call_traits<first_type>::param_type       first_param_type;
+      typedef typename call_traits<second_type>::param_type      second_param_type;
+      typedef typename call_traits<first_type>::reference        first_reference;
+      typedef typename call_traits<second_type>::reference       second_reference;
+      typedef typename call_traits<first_type>::const_reference  first_const_reference;
+      typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+      compressed_pair_imp() {}
+
+      compressed_pair_imp(first_param_type x, second_param_type y)
+         : first_type(x), second_(y) {}
+
+      compressed_pair_imp(first_param_type x)
+         : first_type(x) {}
+
+      compressed_pair_imp(second_param_type y)
+         : second_(y) {}
+
+      first_reference       first()       {return *this;}
+      first_const_reference first() const {return *this;}
+
+      second_reference       second()       {return second_;}
+      second_const_reference second() const {return second_;}
+
+      void swap(::boost::compressed_pair<T1,T2>& y)
+      {
+         // no need to swap empty base class:
+         cp_swap(second_, y.second());
+      }
+   private:
+      second_type second_;
+   };
+
+   // 2    derive from T2
+
+   template <class T1, class T2>
+   class compressed_pair_imp<T1, T2, 2>
+      : private ::boost::remove_cv<T2>::type
+   {
+   public:
+      typedef T1                                                 first_type;
+      typedef T2                                                 second_type;
+      typedef typename call_traits<first_type>::param_type       first_param_type;
+      typedef typename call_traits<second_type>::param_type      second_param_type;
+      typedef typename call_traits<first_type>::reference        first_reference;
+      typedef typename call_traits<second_type>::reference       second_reference;
+      typedef typename call_traits<first_type>::const_reference  first_const_reference;
+      typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+      compressed_pair_imp() {}
+
+      compressed_pair_imp(first_param_type x, second_param_type y)
+         : second_type(y), first_(x) {}
+
+      compressed_pair_imp(first_param_type x)
+         : first_(x) {}
+
+      compressed_pair_imp(second_param_type y)
+         : second_type(y) {}
+
+      first_reference       first()       {return first_;}
+      first_const_reference first() const {return first_;}
+
+      second_reference       second()       {return *this;}
+      second_const_reference second() const {return *this;}
+
+      void swap(::boost::compressed_pair<T1,T2>& y)
+      {
+         // no need to swap empty base class:
+         cp_swap(first_, y.first());
+      }
+
+   private:
+      first_type first_;
+   };
+
+   // 3    derive from T1 and T2
+
+   template <class T1, class T2>
+   class compressed_pair_imp<T1, T2, 3>
+      : private ::boost::remove_cv<T1>::type,
+        private ::boost::remove_cv<T2>::type
+   {
+   public:
+      typedef T1                                                 first_type;
+      typedef T2                                                 second_type;
+      typedef typename call_traits<first_type>::param_type       first_param_type;
+      typedef typename call_traits<second_type>::param_type      second_param_type;
+      typedef typename call_traits<first_type>::reference        first_reference;
+      typedef typename call_traits<second_type>::reference       second_reference;
+      typedef typename call_traits<first_type>::const_reference  first_const_reference;
+      typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+      compressed_pair_imp() {}
+
+      compressed_pair_imp(first_param_type x, second_param_type y)
+         : first_type(x), second_type(y) {}
+
+      compressed_pair_imp(first_param_type x)
+         : first_type(x) {}
+
+      compressed_pair_imp(second_param_type y)
+         : second_type(y) {}
+
+      first_reference       first()       {return *this;}
+      first_const_reference first() const {return *this;}
+
+      second_reference       second()       {return *this;}
+      second_const_reference second() const {return *this;}
+      //
+      // no need to swap empty bases:
+      void swap(::boost::compressed_pair<T1,T2>&) {}
+   };
+
+   // JM
+   // 4    T1 == T2, T1 and T2 both empty
+   //      Note does not actually store an instance of T2 at all -
+   //      but reuses T1 base class for both first() and second().
+   template <class T1, class T2>
+   class compressed_pair_imp<T1, T2, 4>
+      : private ::boost::remove_cv<T1>::type
+   {
+   public:
+      typedef T1                                                 first_type;
+      typedef T2                                                 second_type;
+      typedef typename call_traits<first_type>::param_type       first_param_type;
+      typedef typename call_traits<second_type>::param_type      second_param_type;
+      typedef typename call_traits<first_type>::reference        first_reference;
+      typedef typename call_traits<second_type>::reference       second_reference;
+      typedef typename call_traits<first_type>::const_reference  first_const_reference;
+      typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+      compressed_pair_imp() {}
+
+      compressed_pair_imp(first_param_type x, second_param_type y)
+         : first_type(x), m_second(y) {}
+
+      compressed_pair_imp(first_param_type x)
+         : first_type(x), m_second(x) {}
+
+      first_reference       first()       {return *this;}
+      first_const_reference first() const {return *this;}
+
+      second_reference       second()       {return m_second;}
+      second_const_reference second() const {return m_second;}
+
+      void swap(::boost::compressed_pair<T1,T2>&) {}
+   private:
+      T2 m_second;
+   };
+
+   // 5    T1 == T2 and are not empty:   //JM
+
+   template <class T1, class T2>
+   class compressed_pair_imp<T1, T2, 5>
+   {
+   public:
+      typedef T1                                                 first_type;
+      typedef T2                                                 second_type;
+      typedef typename call_traits<first_type>::param_type       first_param_type;
+      typedef typename call_traits<second_type>::param_type      second_param_type;
+      typedef typename call_traits<first_type>::reference        first_reference;
+      typedef typename call_traits<second_type>::reference       second_reference;
+      typedef typename call_traits<first_type>::const_reference  first_const_reference;
+      typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+      compressed_pair_imp() {}
+
+      compressed_pair_imp(first_param_type x, second_param_type y)
+         : first_(x), second_(y) {}
+
+      compressed_pair_imp(first_param_type x)
+         : first_(x), second_(x) {}
+
+      first_reference       first()       {return first_;}
+      first_const_reference first() const {return first_;}
+
+      second_reference       second()       {return second_;}
+      second_const_reference second() const {return second_;}
+
+      void swap(::boost::compressed_pair<T1, T2>& y)
+      {
+         cp_swap(first_, y.first());
+         cp_swap(second_, y.second());
+      }
+   private:
+      first_type first_;
+      second_type second_;
+   };
+
+}  // details
+
+template <class T1, class T2>
+class compressed_pair
+   : private ::boost::details::compressed_pair_imp<T1, T2,
+             ::boost::details::compressed_pair_switch<
+                    T1,
+                    T2,
+                    ::boost::is_same<typename remove_cv<T1>::type, typename remove_cv<T2>::type>::value,
+                    ::boost::is_empty<T1>::value,
+                    ::boost::is_empty<T2>::value>::value>
+{
+private:
+   typedef details::compressed_pair_imp<T1, T2,
+             ::boost::details::compressed_pair_switch<
+                    T1,
+                    T2,
+                    ::boost::is_same<typename remove_cv<T1>::type, typename remove_cv<T2>::type>::value,
+                    ::boost::is_empty<T1>::value,
+                    ::boost::is_empty<T2>::value>::value> base;
+public:
+   typedef T1                                                 first_type;
+   typedef T2                                                 second_type;
+   typedef typename call_traits<first_type>::param_type       first_param_type;
+   typedef typename call_traits<second_type>::param_type      second_param_type;
+   typedef typename call_traits<first_type>::reference        first_reference;
+   typedef typename call_traits<second_type>::reference       second_reference;
+   typedef typename call_traits<first_type>::const_reference  first_const_reference;
+   typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+            compressed_pair() : base() {}
+            compressed_pair(first_param_type x, second_param_type y) : base(x, y) {}
+   explicit compressed_pair(first_param_type x) : base(x) {}
+   explicit compressed_pair(second_param_type y) : base(y) {}
+
+   first_reference       first()       {return base::first();}
+   first_const_reference first() const {return base::first();}
+
+   second_reference       second()       {return base::second();}
+   second_const_reference second() const {return base::second();}
+
+   void swap(compressed_pair& y) { base::swap(y); }
+};
+
+// JM
+// Partial specialisation for case where T1 == T2:
+//
+template <class T>
+class compressed_pair<T, T>
+   : private details::compressed_pair_imp<T, T,
+             ::boost::details::compressed_pair_switch<
+                    T,
+                    T,
+                    ::boost::is_same<typename remove_cv<T>::type, typename remove_cv<T>::type>::value,
+                    ::boost::is_empty<T>::value,
+                    ::boost::is_empty<T>::value>::value>
+{
+private:
+   typedef details::compressed_pair_imp<T, T,
+             ::boost::details::compressed_pair_switch<
+                    T,
+                    T,
+                    ::boost::is_same<typename remove_cv<T>::type, typename remove_cv<T>::type>::value,
+                    ::boost::is_empty<T>::value,
+                    ::boost::is_empty<T>::value>::value> base;
+public:
+   typedef T                                                  first_type;
+   typedef T                                                  second_type;
+   typedef typename call_traits<first_type>::param_type       first_param_type;
+   typedef typename call_traits<second_type>::param_type      second_param_type;
+   typedef typename call_traits<first_type>::reference        first_reference;
+   typedef typename call_traits<second_type>::reference       second_reference;
+   typedef typename call_traits<first_type>::const_reference  first_const_reference;
+   typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+            compressed_pair() : base() {}
+            compressed_pair(first_param_type x, second_param_type y) : base(x, y) {}
+#if !(defined(__SUNPRO_CC) && (__SUNPRO_CC <= 0x530))
+   explicit 
+#endif
+      compressed_pair(first_param_type x) : base(x) {}
+
+   first_reference       first()       {return base::first();}
+   first_const_reference first() const {return base::first();}
+
+   second_reference       second()       {return base::second();}
+   second_const_reference second() const {return base::second();}
+
+   void swap(::boost::compressed_pair<T,T>& y) { base::swap(y); }
+};
+
+template <class T1, class T2>
+inline
+void
+swap(compressed_pair<T1, T2>& x, compressed_pair<T1, T2>& y)
+{
+   x.swap(y);
+}
+
+} // boost
+
+#endif // BOOST_DETAIL_COMPRESSED_PAIR_HPP
+
--- a/include/boost/detail/ob_call_traits.hpp
+++ b/include/boost/detail/ob_call_traits.hpp
@@ -0,0 +1,168 @@
+//  (C) Copyright Steve Cleary, Beman Dawes, Howard Hinnant & John Maddock 2000.
+//  Use, modification and distribution are subject to the Boost Software License,
+//  Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt).
+//
+//  See http://www.boost.org/libs/utility for most recent version including documentation.
+//
+//  Crippled version for crippled compilers:
+//  see libs/utility/call_traits.htm
+//
+
+/* Release notes:
+   01st October 2000:
+      Fixed call_traits on VC6, using "poor man's partial specialisation",
+      using ideas taken from "Generative programming" by Krzysztof Czarnecki 
+      & Ulrich Eisenecker.
+*/
+
+#ifndef BOOST_OB_CALL_TRAITS_HPP
+#define BOOST_OB_CALL_TRAITS_HPP
+
+#ifndef BOOST_CONFIG_HPP
+#include <boost/config.hpp>
+#endif
+
+#ifndef BOOST_ARITHMETIC_TYPE_TRAITS_HPP
+#include <boost/type_traits/arithmetic_traits.hpp>
+#endif
+#ifndef BOOST_COMPOSITE_TYPE_TRAITS_HPP
+#include <boost/type_traits/composite_traits.hpp>
+#endif
+
+namespace boost{
+
+#ifdef BOOST_MSVC6_MEMBER_TEMPLATES
+//
+// use member templates to emulate
+// partial specialisation:
+//
+namespace detail{
+
+template <class T>
+struct standard_call_traits
+{
+   typedef T value_type;
+   typedef T& reference;
+   typedef const T& const_reference;
+   typedef const T& param_type;
+};
+template <class T>
+struct simple_call_traits
+{
+   typedef T value_type;
+   typedef T& reference;
+   typedef const T& const_reference;
+   typedef const T param_type;
+};
+template <class T>
+struct reference_call_traits
+{
+   typedef T value_type;
+   typedef T reference;
+   typedef T const_reference;
+   typedef T param_type;
+};
+
+template <bool pointer, bool arithmetic, bool reference>
+struct call_traits_chooser
+{
+   template <class T>
+   struct rebind
+   {
+      typedef standard_call_traits<T> type;
+   };
+};
+
+template <>
+struct call_traits_chooser<true, false, false>
+{
+   template <class T>
+   struct rebind
+   {
+      typedef simple_call_traits<T> type;
+   };
+};
+
+template <>
+struct call_traits_chooser<false, false, true>
+{
+   template <class T>
+   struct rebind
+   {
+      typedef reference_call_traits<T> type;
+   };
+};
+
+template <bool size_is_small> 
+struct call_traits_sizeof_chooser2
+{
+   template <class T>
+   struct small_rebind
+   {
+      typedef simple_call_traits<T> small_type;
+   };
+};
+
+template<> 
+struct call_traits_sizeof_chooser2<false>
+{
+   template <class T>
+   struct small_rebind
+   {
+      typedef standard_call_traits<T> small_type;
+   };
+};
+
+template <>
+struct call_traits_chooser<false, true, false>
+{
+   template <class T>
+   struct rebind
+   {
+      enum { sizeof_choice = (sizeof(T) <= sizeof(void*)) };
+      typedef call_traits_sizeof_chooser2<(sizeof(T) <= sizeof(void*))> chooser;
+      typedef typename chooser::template small_rebind<T> bound_type;
+      typedef typename bound_type::small_type type;
+   };
+};
+
+} // namespace detail
+template <typename T>
+struct call_traits
+{
+private:
+    typedef detail::call_traits_chooser<
+         ::boost::is_pointer<T>::value,
+         ::boost::is_arithmetic<T>::value, 
+         ::boost::is_reference<T>::value
+      > chooser;
+   typedef typename chooser::template rebind<T> bound_type;
+   typedef typename bound_type::type call_traits_type;
+public:
+   typedef typename call_traits_type::value_type       value_type;
+   typedef typename call_traits_type::reference        reference;
+   typedef typename call_traits_type::const_reference  const_reference;
+   typedef typename call_traits_type::param_type       param_type;
+};
+
+#else
+//
+// sorry call_traits is completely non-functional
+// blame your broken compiler:
+//
+
+template <typename T>
+struct call_traits
+{
+   typedef T value_type;
+   typedef T& reference;
+   typedef const T& const_reference;
+   typedef const T& param_type;
+};
+
+#endif // member templates
+
+}
+
+#endif // BOOST_OB_CALL_TRAITS_HPP
--- a/include/boost/detail/ob_compressed_pair.hpp
+++ b/include/boost/detail/ob_compressed_pair.hpp
@@ -0,0 +1,510 @@
+//  (C) Copyright Steve Cleary, Beman Dawes, Howard Hinnant & John Maddock 2000.
+//  Use, modification and distribution are subject to the Boost Software License,
+//  Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt).
+//
+//  See http://www.boost.org/libs/utility for most recent version including documentation.
+//  see libs/utility/compressed_pair.hpp
+//
+/* Release notes:
+   20 Jan 2001:
+        Fixed obvious bugs (David Abrahams)
+   07 Oct 2000:
+      Added better single argument constructor support.
+   03 Oct 2000:
+      Added VC6 support (JM).
+   23rd July 2000:
+      Additional comments added. (JM)
+   Jan 2000:
+      Original version: this version crippled for use with crippled compilers
+      - John Maddock Jan 2000.
+*/
+
+
+#ifndef BOOST_OB_COMPRESSED_PAIR_HPP
+#define BOOST_OB_COMPRESSED_PAIR_HPP
+
+#include <algorithm>
+#ifndef BOOST_OBJECT_TYPE_TRAITS_HPP
+#include <boost/type_traits/object_traits.hpp>
+#endif
+#ifndef BOOST_SAME_TRAITS_HPP
+#include <boost/type_traits/same_traits.hpp>
+#endif
+#ifndef BOOST_CALL_TRAITS_HPP
+#include <boost/call_traits.hpp>
+#endif
+
+namespace boost
+{
+#ifdef BOOST_MSVC6_MEMBER_TEMPLATES
+//
+// use member templates to emulate
+// partial specialisation.  Note that due to
+// problems with overload resolution with VC6
+// each of the compressed_pair versions that follow
+// have one template single-argument constructor
+// in place of two specific constructors:
+//
+
+template <class T1, class T2>
+class compressed_pair;
+
+namespace detail{
+
+template <class A, class T1, class T2>
+struct best_conversion_traits
+{
+   typedef char one;
+   typedef char (&two)[2];
+   static A a;
+   static one test(T1);
+   static two test(T2);
+
+   enum { value = sizeof(test(a)) };
+};
+
+template <int>
+struct init_one;
+
+template <>
+struct init_one<1>
+{
+   template <class A, class T1, class T2>
+   static void init(const A& a, T1* p1, T2*)
+   {
+      *p1 = a;
+   }
+};
+
+template <>
+struct init_one<2>
+{
+   template <class A, class T1, class T2>
+   static void init(const A& a, T1*, T2* p2)
+   {
+      *p2 = a;
+   }
+};
+
+
+// T1 != T2, both non-empty
+template <class T1, class T2>
+class compressed_pair_0
+{
+private:
+   T1 _first;
+   T2 _second;
+public:
+   typedef T1                                                 first_type;
+   typedef T2                                                 second_type;
+   typedef typename call_traits<first_type>::param_type       first_param_type;
+   typedef typename call_traits<second_type>::param_type      second_param_type;
+   typedef typename call_traits<first_type>::reference        first_reference;
+   typedef typename call_traits<second_type>::reference       second_reference;
+   typedef typename call_traits<first_type>::const_reference  first_const_reference;
+   typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+            compressed_pair_0() : _first(), _second() {}
+            compressed_pair_0(first_param_type x, second_param_type y) : _first(x), _second(y) {}
+   template <class A>
+   explicit compressed_pair_0(const A& val)
+   {
+      init_one<best_conversion_traits<A, T1, T2>::value>::init(val, &_first, &_second);
+   }
+   compressed_pair_0(const ::boost::compressed_pair<T1,T2>& x)
+      : _first(x.first()), _second(x.second()) {}
+
+#if 0
+  compressed_pair_0& operator=(const compressed_pair_0& x) {
+    cout << "assigning compressed pair 0" << endl;
+    _first = x._first;
+    _second = x._second;
+    cout << "finished assigning compressed pair 0" << endl;
+    return *this;
+  }
+#endif
+
+   first_reference       first()       { return _first; }
+   first_const_reference first() const { return _first; }
+
+   second_reference       second()       { return _second; }
+   second_const_reference second() const { return _second; }
+
+   void swap(compressed_pair_0& y)
+   {
+      using std::swap;
+      swap(_first, y._first);
+      swap(_second, y._second);
+   }
+};
+
+// T1 != T2, T2 empty
+template <class T1, class T2>
+class compressed_pair_1 : T2
+{
+private:
+   T1 _first;
+public:
+   typedef T1                                                 first_type;
+   typedef T2                                                 second_type;
+   typedef typename call_traits<first_type>::param_type       first_param_type;
+   typedef typename call_traits<second_type>::param_type      second_param_type;
+   typedef typename call_traits<first_type>::reference        first_reference;
+   typedef typename call_traits<second_type>::reference       second_reference;
+   typedef typename call_traits<first_type>::const_reference  first_const_reference;
+   typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+            compressed_pair_1() : T2(), _first() {}
+            compressed_pair_1(first_param_type x, second_param_type y) : T2(y), _first(x) {}
+
+   template <class A>
+   explicit compressed_pair_1(const A& val)
+   {
+      init_one<best_conversion_traits<A, T1, T2>::value>::init(val, &_first, static_cast<T2*>(this));
+   }
+
+   compressed_pair_1(const ::boost::compressed_pair<T1,T2>& x)
+      : T2(x.second()), _first(x.first()) {}
+
+#if defined(BOOST_MSVC) && BOOST_MSVC <= 1300
+  // Total weirdness. If the assignment to _first is moved after
+  // the call to the inherited operator=, then this breaks graph/test/graph.cpp
+  // by way of iterator_adaptor.
+  compressed_pair_1& operator=(const compressed_pair_1& x) {
+    _first = x._first;
+    T2::operator=(x);
+    return *this;
+  }
+#endif
+
+   first_reference       first()       { return _first; }
+   first_const_reference first() const { return _first; }
+
+   second_reference       second()       { return *this; }
+   second_const_reference second() const { return *this; }
+
+   void swap(compressed_pair_1& y)
+   {
+      // no need to swap empty base class:
+      using std::swap;
+      swap(_first, y._first);
+   }
+};
+
+// T1 != T2, T1 empty
+template <class T1, class T2>
+class compressed_pair_2 : T1
+{
+private:
+   T2 _second;
+public:
+   typedef T1                                                 first_type;
+   typedef T2                                                 second_type;
+   typedef typename call_traits<first_type>::param_type       first_param_type;
+   typedef typename call_traits<second_type>::param_type      second_param_type;
+   typedef typename call_traits<first_type>::reference        first_reference;
+   typedef typename call_traits<second_type>::reference       second_reference;
+   typedef typename call_traits<first_type>::const_reference  first_const_reference;
+   typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+            compressed_pair_2() : T1(), _second() {}
+            compressed_pair_2(first_param_type x, second_param_type y) : T1(x), _second(y) {}
+   template <class A>
+   explicit compressed_pair_2(const A& val)
+   {
+      init_one<best_conversion_traits<A, T1, T2>::value>::init(val, static_cast<T1*>(this), &_second);
+   }
+   compressed_pair_2(const ::boost::compressed_pair<T1,T2>& x)
+      : T1(x.first()), _second(x.second()) {}
+
+#if 0
+  compressed_pair_2& operator=(const compressed_pair_2& x) {
+    cout << "assigning compressed pair 2" << endl;
+    T1::operator=(x);
+    _second = x._second;
+    cout << "finished assigning compressed pair 2" << endl;
+    return *this;
+  }
+#endif
+   first_reference       first()       { return *this; }
+   first_const_reference first() const { return *this; }
+
+   second_reference       second()       { return _second; }
+   second_const_reference second() const { return _second; }
+
+   void swap(compressed_pair_2& y)
+   {
+      // no need to swap empty base class:
+      using std::swap;
+      swap(_second, y._second);
+   }
+};
+
+// T1 != T2, both empty
+template <class T1, class T2>
+class compressed_pair_3 : T1, T2
+{
+public:
+   typedef T1                                                 first_type;
+   typedef T2                                                 second_type;
+   typedef typename call_traits<first_type>::param_type       first_param_type;
+   typedef typename call_traits<second_type>::param_type      second_param_type;
+   typedef typename call_traits<first_type>::reference        first_reference;
+   typedef typename call_traits<second_type>::reference       second_reference;
+   typedef typename call_traits<first_type>::const_reference  first_const_reference;
+   typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+            compressed_pair_3() : T1(), T2() {}
+            compressed_pair_3(first_param_type x, second_param_type y) : T1(x), T2(y) {}
+   template <class A>
+   explicit compressed_pair_3(const A& val)
+   {
+      init_one<best_conversion_traits<A, T1, T2>::value>::init(val, static_cast<T1*>(this), static_cast<T2*>(this));
+   }
+   compressed_pair_3(const ::boost::compressed_pair<T1,T2>& x)
+      : T1(x.first()), T2(x.second()) {}
+
+   first_reference       first()       { return *this; }
+   first_const_reference first() const { return *this; }
+
+   second_reference       second()       { return *this; }
+   second_const_reference second() const { return *this; }
+
+   void swap(compressed_pair_3& y)
+   {
+      // no need to swap empty base classes:
+   }
+};
+
+// T1 == T2, and empty
+template <class T1, class T2>
+class compressed_pair_4 : T1
+{
+public:
+   typedef T1                                                 first_type;
+   typedef T2                                                 second_type;
+   typedef typename call_traits<first_type>::param_type       first_param_type;
+   typedef typename call_traits<second_type>::param_type      second_param_type;
+   typedef typename call_traits<first_type>::reference        first_reference;
+   typedef typename call_traits<second_type>::reference       second_reference;
+   typedef typename call_traits<first_type>::const_reference  first_const_reference;
+   typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+            compressed_pair_4() : T1() {}
+            compressed_pair_4(first_param_type x, second_param_type y) : T1(x), m_second(y) {}
+   // only one single argument constructor since T1 == T2
+   explicit compressed_pair_4(first_param_type x) : T1(x), m_second(x) {}
+   compressed_pair_4(const ::boost::compressed_pair<T1,T2>& x)
+      : T1(x.first()), m_second(x.second()) {}
+
+   first_reference       first()       { return *this; }
+   first_const_reference first() const { return *this; }
+
+   second_reference       second()       { return m_second; }
+   second_const_reference second() const { return m_second; }
+
+   void swap(compressed_pair_4& y)
+   {
+      // no need to swap empty base classes:
+   }
+private:
+   T2 m_second;
+};
+
+// T1 == T2, not empty
+template <class T1, class T2>
+class compressed_pair_5
+{
+private:
+   T1 _first;
+   T2 _second;
+public:
+   typedef T1                                                 first_type;
+   typedef T2                                                 second_type;
+   typedef typename call_traits<first_type>::param_type       first_param_type;
+   typedef typename call_traits<second_type>::param_type      second_param_type;
+   typedef typename call_traits<first_type>::reference        first_reference;
+   typedef typename call_traits<second_type>::reference       second_reference;
+   typedef typename call_traits<first_type>::const_reference  first_const_reference;
+   typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+            compressed_pair_5() : _first(), _second() {}
+            compressed_pair_5(first_param_type x, second_param_type y) : _first(x), _second(y) {}
+   // only one single argument constructor since T1 == T2
+   explicit compressed_pair_5(first_param_type x) : _first(x), _second(x) {}
+   compressed_pair_5(const ::boost::compressed_pair<T1,T2>& c) 
+      : _first(c.first()), _second(c.second()) {}
+
+   first_reference       first()       { return _first; }
+   first_const_reference first() const { return _first; }
+
+   second_reference       second()       { return _second; }
+   second_const_reference second() const { return _second; }
+
+   void swap(compressed_pair_5& y)
+   {
+      using std::swap;
+      swap(_first, y._first);
+      swap(_second, y._second);
+   }
+};
+
+template <bool e1, bool e2, bool same>
+struct compressed_pair_chooser
+{
+   template <class T1, class T2>
+   struct rebind
+   {
+      typedef compressed_pair_0<T1, T2> type;
+   };
+};
+
+template <>
+struct compressed_pair_chooser<false, true, false>
+{
+   template <class T1, class T2>
+   struct rebind
+   {
+      typedef compressed_pair_1<T1, T2> type;
+   };
+};
+
+template <>
+struct compressed_pair_chooser<true, false, false>
+{
+   template <class T1, class T2>
+   struct rebind
+   {
+      typedef compressed_pair_2<T1, T2> type;
+   };
+};
+
+template <>
+struct compressed_pair_chooser<true, true, false>
+{
+   template <class T1, class T2>
+   struct rebind
+   {
+      typedef compressed_pair_3<T1, T2> type;
+   };
+};
+
+template <>
+struct compressed_pair_chooser<true, true, true>
+{
+   template <class T1, class T2>
+   struct rebind
+   {
+      typedef compressed_pair_4<T1, T2> type;
+   };
+};
+
+template <>
+struct compressed_pair_chooser<false, false, true>
+{
+   template <class T1, class T2>
+   struct rebind
+   {
+      typedef compressed_pair_5<T1, T2> type;
+   };
+};
+
+template <class T1, class T2>
+struct compressed_pair_traits
+{
+private:
+   typedef compressed_pair_chooser<is_empty<T1>::value, is_empty<T2>::value, is_same<T1,T2>::value> chooser;
+   typedef typename chooser::template rebind<T1, T2> bound_type;
+public:
+   typedef typename bound_type::type type;
+};
+
+} // namespace detail
+
+template <class T1, class T2>
+class compressed_pair : public detail::compressed_pair_traits<T1, T2>::type
+{
+private:
+   typedef typename detail::compressed_pair_traits<T1, T2>::type base_type;
+public:
+   typedef T1                                                 first_type;
+   typedef T2                                                 second_type;
+   typedef typename call_traits<first_type>::param_type       first_param_type;
+   typedef typename call_traits<second_type>::param_type      second_param_type;
+   typedef typename call_traits<first_type>::reference        first_reference;
+   typedef typename call_traits<second_type>::reference       second_reference;
+   typedef typename call_traits<first_type>::const_reference  first_const_reference;
+   typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+            compressed_pair() : base_type() {}
+            compressed_pair(first_param_type x, second_param_type y) : base_type(x, y) {}
+   template <class A>
+   explicit compressed_pair(const A& x) : base_type(x){}
+
+   first_reference       first()       { return base_type::first(); }
+   first_const_reference first() const { return base_type::first(); }
+
+   second_reference       second()       { return base_type::second(); }
+   second_const_reference second() const { return base_type::second(); }
+};
+
+template <class T1, class T2>
+inline void swap(compressed_pair<T1, T2>& x, compressed_pair<T1, T2>& y)
+{
+   x.swap(y);
+}
+
+#else
+// no partial specialisation, no member templates:
+
+template <class T1, class T2>
+class compressed_pair
+{
+private:
+   T1 _first;
+   T2 _second;
+public:
+   typedef T1                                                 first_type;
+   typedef T2                                                 second_type;
+   typedef typename call_traits<first_type>::param_type       first_param_type;
+   typedef typename call_traits<second_type>::param_type      second_param_type;
+   typedef typename call_traits<first_type>::reference        first_reference;
+   typedef typename call_traits<second_type>::reference       second_reference;
+   typedef typename call_traits<first_type>::const_reference  first_const_reference;
+   typedef typename call_traits<second_type>::const_reference second_const_reference;
+
+            compressed_pair() : _first(), _second() {}
+            compressed_pair(first_param_type x, second_param_type y) : _first(x), _second(y) {}
+   explicit compressed_pair(first_param_type x) : _first(x), _second() {}
+   // can't define this in case T1 == T2:
+   // explicit compressed_pair(second_param_type y) : _first(), _second(y) {}
+
+   first_reference       first()       { return _first; }
+   first_const_reference first() const { return _first; }
+
+   second_reference       second()       { return _second; }
+   second_const_reference second() const { return _second; }
+
+   void swap(compressed_pair& y)
+   {
+      using std::swap;
+      swap(_first, y._first);
+      swap(_second, y._second);
+   }
+};
+
+template <class T1, class T2>
+inline void swap(compressed_pair<T1, T2>& x, compressed_pair<T1, T2>& y)
+{
+   x.swap(y);
+}
+
+#endif
+
+} // boost
+
+#endif // BOOST_OB_COMPRESSED_PAIR_HPP
+
+
+