From 1972959fda899a0ba93526d1a616e0ec381c4ce7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jaakko=20J=C3=A4rvi?= <jarvi@cs.tamu.edu>
Date: Wed, 26 Feb 2003 23:10:55 +0000
Subject: [PATCH] element<T>::type takes constness into consideration

[SVN r17666]
---
 doc/tuple_advanced_interface.html          |  4 +++-
 include/boost/tuple/detail/tuple_basic.hpp | 15 +++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/doc/tuple_advanced_interface.html b/doc/tuple_advanced_interface.html
index 1b9df5a..a8cfc5c 100644
--- a/doc/tuple_advanced_interface.html
+++ b/doc/tuple_advanced_interface.html
@@ -20,7 +20,9 @@ Suppose <code>T</code> is a tuple type, and <code>N</code> is a constant integra
 
 <code><pre>element&lt;N, T&gt;::type</pre></code>
 
-gives the type of the <code>N</code>th element in the tuple type <code>T</code>.
+gives the type of the <code>N</code>th element in the tuple type <code>T</code>. If <code>T</code> is const, the resulting type is const qualified as well. 
+Note that the constness of <code>T</code> does not affect reference type
+elements.
 </p>
 
 <code><pre>length&lt;T&gt;::value</pre></code>
diff --git a/include/boost/tuple/detail/tuple_basic.hpp b/include/boost/tuple/detail/tuple_basic.hpp
index acc25b9..22478c6 100644
--- a/include/boost/tuple/detail/tuple_basic.hpp
+++ b/include/boost/tuple/detail/tuple_basic.hpp
@@ -153,6 +153,21 @@ struct element<0,T>
   typedef typename T::head_type type;
 };
 
+template<int N, class T>
+struct element<N, const T>
+{
+private:
+  typedef typename T::tail_type Next;
+  typedef typename element<N-1, Next>::type unqualified_type;
+public:
+  typedef typename boost::add_const<unqualified_type>::type type;
+};
+template<class T>
+struct element<0,const T>
+{
+  typedef typename boost::add_const<typename T::head_type>::type type;
+};
+
 // -get function templates -----------------------------------------------
 // Usage: get<N>(aTuple)