Static `if'.

- mlc/if.hh: New file.


git-svn-id: https://svn.lrde.epita.fr/svn/oln/trunk@387 4aad255d-cdde-0310-9447-f3009e2ae8c0

metalic/ChangeLog

+2006-01-26  Roland Levillain  <roland@lrde.epita.fr>
+
+	Static `if'.
+
+	* mlc/if.hh: New file.
+
 2006-01-26  Thierry Geraud  <theo@lrde.epita.fr>
 
 	Add mlc::ensure_ and update. .

metalic/mlc/if.hh

+// Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006 EPITA Research and Development Laboratory
+//
+// This file is part of the Olena Library.  This library is free
+// software; you can redistribute it and/or modify it under the terms
+// of the GNU General Public License version 2 as published by the
+// Free Software Foundation.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this library; see the file COPYING.  If not, write to
+// the Free Software Foundation, 59 Temple Place - Suite 330, Boston,
+// MA 02111-1307, USA.
+//
+// As a special exception, you may use this file as part of a free
+// software library without restriction.  Specifically, if other files
+// instantiate templates or use macros or inline functions from this
+// file, or you compile this file and link it with other files to
+// produce an executable, this file does not by itself cause the
+// resulting executable to be covered by the GNU General Public
+// License.  This exception does not however invalidate any other
+// reasons why the executable file might be covered by the GNU General
+// Public License.
+
+#ifndef METALIC_IF_HH
+# define METALIC_IF_HH
+
+# include <mlc/bool.hh>
+
+
+/** \def mlc_if(Cond, Then, Else)
+ ** \brief Static `if' on types.
+ **
+ ** If \a Cond is true, evaluate to type \a Then, otherwise evaluate to
+ ** type \a Else.
+ **
+ ** \note \a Then and \a Else must be valid types, since they are both
+ ** evaluated, whatever the result of \a Cond.
+ **
+ */
+# define mlc_if(Cond, Then, Else)  typename mlc::if_<Cond, Then, Else>::ret
+/// Likewise, without the leading \c typename keyword.
+# define mlc_if_(Cond, Then, Else)          mlc::if_<Cond, Then, Else>::ret
+
+
+namespace mlc
+{
+
+  namespace internal
+  {
+
+    /// \brief Declare a static `if'.
+    /// \note Internal class, don't use it directly.
+    template <bool b, typename then_type, typename else_type>
+    struct if_;
+
+    /// \brief Specialization of mlc::internal::if_ when condition is true.
+    /// \note Internal class, don't use it directly.
+    template <typename then_type, typename else_type>
+    struct if_ <true, then_type, else_type>
+    {
+      typedef then_type ret;
+    };
+    
+    /// \brief Specialization of mlc::internal::if_ when condition is false.
+    /// \note Internal class, don't use it directly.
+    template <typename then_type, typename else_type>
+    struct if_ <false, then_type, else_type>
+    {
+      typedef else_type ret;
+    };
+    
+  } // end of namespace mlc::internal
+
+
+/** \brief Static `if' on types.
+ **
+ ** If \a Cond is true, evaluate to type \a Then, otherwise evaluate to
+ ** type \a Else.  The \a ret member holds the result.
+ **
+ ** \note \a Then and \a Else must be valid types, since they are both
+ ** evaluated, whatever the result of \a Cond.
+ */
+  template <typename cond_type, typename then_type, typename else_type>
+  struct if_ : public internal::if_ < mlc_bool(cond_type), then_type, else_type >
+  {
+  };
+
+} // end of namespace mlc
+
+
+#endif // ! METALIC_IF_HH