[Rprotobuf-commits] r897 - papers/jss

[noreply at r-forge.r-project.org]

Author: murray
Date: 2014-09-25 07:36:52 +0200 (Thu, 25 Sep 2014)
New Revision: 897

Modified:
   papers/jss/article.Rnw
Log:
Address some reviewer feedback about why we use RObjectTables and some
of the pitfalls, with some of this text provided verbatim from Karl
Millar, who is already thanked in the acknowledgements section.



Modified: papers/jss/article.Rnw
===================================================================
--- papers/jss/article.Rnw	2014-09-16 01:34:29 UTC (rev 896)
+++ papers/jss/article.Rnw	2014-09-25 05:36:52 UTC (rev 897)
@@ -359,8 +359,12 @@
 \subsection[Importing message descriptors from .proto files]{Importing message descriptors from \code{.proto} files}
 
 To create or parse a Protocol Buffer Message, one must first read in 
-the message type specification from a \code{.proto} file. The 
-\code{.proto} files are imported using the \code{readProtoFiles}
+the message type specification from a \code{.proto} file. 
+A small number of message types are imported when the package is first
+loaded, including the \code{tutorial.Person} type we saw in the last
+section.
+All other types must be imported from
+\code{.proto} files using the \code{readProtoFiles}
 function, which can either import a single file, all files in a directory,
 or every \code{.proto} file provided by a particular \proglang{R} package.
 
@@ -371,7 +375,17 @@
 available from the OmegaHat project \citep{RObjectTables}.  Instead of
 being associated with a static hash table, this environment
 dynamically queries the in-memory database of loaded descriptors
-during normal variable lookup.
+during normal variable lookup.  This allows new descriptors to be
+parsed from \code{.proto} files and added to the global
+namespace.\footnote{Note that there is a significant performance
+  overhead with this RObjectTable implementation.  Because the table
+  is on the search path and isn't cacheable, lookups of symbols that
+  are behind it in the search path can't be added to the global object
+  cache, and R must perform an expensive lookup through all of the
+  attached environments and the protocol buffer definitions to find common
+  symbols (most notably those in base) from the global environment.
+  Fortunately, proper use of namespaces and package imports reduces
+  the impact of this for code in packages.}
 
 <<>>=
 ls("RProtoBuf:DescriptorPool")