extent: add typecasting member function

Makefile.am

@@ -27,6 +27,7 @@ UTIL_FILES   =		\
     exe.hpp		\
     extent.cpp		\
     extent.hpp		\
+    extent.ipp		\
     fixed.cpp		\
     fixed.hpp		\
     float.cpp		\

extent.hpp

@@ -45,6 +45,9 @@ namespace util {
         bool operator !=(const extent& rhs) const
             { return !(*this == rhs); }
 
+        template <typename U>
+        extent<U> cast (void) const;
+
         void sanity (void) const;
     };
 }
@@ -52,4 +55,6 @@ namespace util {
 template <typename T>
 std::ostream& operator<< (std::ostream&, util::extent<T>);
 
+#include "extent.ipp"
+
 #endif

extent.ipp

@@ -0,0 +1,37 @@
+/*
+ * This file is part of libgim.
+ *
+ * libgim is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later
+ * version.
+ *
+ * libgim 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 libgim.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Copyright 2015 Danny Robson <danny@nerdcruft.net>
+ */
+
+
+#ifdef __UTIL_EXTENT_IPP
+#error "twice included ipp"
+#endif
+
+#define __UTIL_EXTENT_IPP
+
+//-----------------------------------------------------------------------------
+template <typename T>
+template <typename U>
+util::extent<U>
+util::extent<T>::cast (void) const
+{
+    return {
+        static_cast<U> (w),
+        static_cast<U> (h)
+    };
+}