initial checkin

[SVN r11780]

include/boost/preprocessor/empty.hpp

@@ -0,0 +1,73 @@
+#ifndef BOOST_PREPROCESSOR_EMPTY_HPP
+#define BOOST_PREPROCESSOR_EMPTY_HPP
+
+//  Copyright (C) 2001
+//  Housemarque, Inc.
+//  http://www.housemarque.com
+//  
+//  Permission to copy, use, modify, sell and distribute this software is
+//  granted provided this copyright notice appears in all copies. This
+//  software is provided "as is" without express or implied warranty, and
+//  with no claim as to its suitability for any purpose.
+
+//  See http://www.boost.org for most recent version.
+
+/*! \file
+
+<a href="../../../../boost/preprocessor/empty.hpp">Click here to see the header.</a>
+*/
+
+//! Expands to nothing. Used with BOOST_PREPROCESSOR_IF() and as an unused parameter.
+/*!
+Example usage as the implementation of BOOST_PREPROCESSOR_COMMA_IF(C):
+
+<PRE>\verbatim
+  #define BOOST_PREPROCESSOR_COMMA_IF(C)\
+    BOOST_PREPROCESSOR_IF(C,BOOST_PREPROCESSOR_COMMA,BOOST_PREPROCESSOR_EMPTY)()
+\endverbatim</PRE>
+
+Example usage as an unused macro parameter:
+
+<PRE>\verbatim
+  #define BOOST_PREPROCESSOR_DEF(CV)\
+    template<class base>            \
+    CV typename implement_subscript_using_begin_subscript<base>::value_type&\
+      implement_subscript_using_begin_subscript<base>::operator[]\
+      ( index_type                  \
+          i                         \
+      ) CV                          \
+    { return base::begin()[i];      \
+    }
+
+  BOOST_PREPROCESSOR_DEF(BOOST_PREPROCESSOR_EMPTY())
+  BOOST_PREPROCESSOR_DEF(const)
+  #undef BOOST_PREPROCESSOR_DEF
+\endverbatim</PRE>
+
+The above expands to:
+
+<PRE>\verbatim
+  template<class base>
+  typename implement_subscript_using_begin_subscript<base>::value_type&
+    implement_subscript_using_begin_subscript<base>::operator[]
+    ( index_type
+        i
+    )
+  { return base::begin()[i];
+  }
+
+  template<class base>
+  const typename implement_subscript_using_begin_subscript<base>::value_type&
+    implement_subscript_using_begin_subscript<base>::operator[]
+    ( index_type
+        i
+    ) const
+  { return base::begin()[i];
+  }
+\endverbatim</PRE>
+
+In case you wonder, the above code is part of a generalized layer for
+implementing the subscripting operators of a random access container.
+*/
+#define BOOST_PREPROCESSOR_EMPTY()
+#endif