Merge pull request #1021 from skyfex/devel

Added documentation for packed pragma

doc/manual.txt

@@ -5390,6 +5390,16 @@ checked.
 **Future directions**: GC'ed memory should be allowed in unions and the GC
 should scan unions conservatively.
 
+Packed pragma
+-------------
+The `packed`:idx: pragma can be applied to any ``object`` type. It ensures 
+that the fields of an object are packed back-to-back in memory. It is useful 
+to store packets or messages from/to network or hardware drivers, and for 
+interoperability with C. Combining packed pragma with inheritance is not 
+defined, and it should not be used with GC'ed memory (ref's).  
+
+**Future directions**: Using GC'ed memory in packed pragma will result in 
+compile-time error. Usage with inheritance should be defined and documented.
 
 Unchecked pragma
 ----------------

web/news.txt

@@ -61,6 +61,8 @@ News
       evaluation.
     - ``--gc:none`` produces warnings when code uses the GC.
     - A ``union`` pragma for better C interoperability is now supported.
+    - A ``packed`` pragma to control the memory packing/alignment of fields in 
+      an object.
     - Arrays can be annotated to be ``unchecked`` for easier low level
       manipulations of memory.