Merge pull request #1009 from RcppCore/feature/rcpp_faq_addition

two (short) new entries for Rcpp-FAQ vignette

Author: eddelbuettel

ChangeLog

@@ -18,6 +18,9 @@
 
 	* inst/unitTests/runit.exposeClass.R: Updated to pass with r-devel
 
+	* vignettes/rmd/Rcpp-FAQ.Rmd: Two new short section on speedier
+	compilation and lack of exceptions / stop() across shared libraries
+
 2019-10-26  Dirk Eddelbuettel  <[email protected]>
 
 	* vignettes/Rcpp-package.Rnw: Another wrapper

vignettes/rmd/Rcpp-FAQ.Rmd

@@ -1206,6 +1206,23 @@ helps within this environment as it installs the corresponding
 systems is provided
 [at this page](https://conda.io/docs/user-guide/tasks/build-packages/compiler-tools.html).
 
+## Can I speed up compilation?
+
+Somewhat. One option is to cache as much as possible via
+[ccache](https://ccache.dev/) by adding it to `~/.R/Makevars`.
+
+Depending on what parts of Rcpp are being used, compilation speed can be
+increased by turning use of Modules off.  Starting with version 1.0.3, the
+`RCPP_NO_MODULES` define can be used. It can be set in `src/Makevars` as
+an argument to `PKG_CXXFLAGS` (or one of the other C++ dialect options) as
+`-DRCPP_NO_MODULES`. This has the advantage of affecting _all_ files in the
+package, including the auto-generated `RcppExports.cpp` where it might be
+trickier to set it manually.
+
+Beyond modules, RTTI support can also be turned off. this implies turning
+Modules support off as well so. To select this approach, use the
+`RCPP_NO_RTTI` define.
+
 # Support
 
 ## Is the API documented
@@ -1720,3 +1737,20 @@ elsewhere.
 So if your autogenerated file fails, and a `symbols not found` error is reported
 by the linker, consider running `compileAttributes()` twice. Deleting
 `R/RcppExports.R` and `src/RcppExports.cpp` may also work.
+
+## Can we use exceptions and stop() across shared libraries?
+
+Within limits, yes. Code that is generated via Rcpp Attributes (see
+\citet{CRAN:Rcpp:Attributes} and Section~\ref{using-attributes}) generally
+handles this correctly and gracefully via the `try-catch` layer it adds
+shielding the exception from propagating to another, separate dynamic
+library.
+
+However, this mechanism relies on dynamic linking with the (system library)
+`libgcc` providing the C++ standard library (as well as on using the same C++
+standard library across all compiled components). But this library is linked
+statically on Windows putting a limitation on the use of `stop()` from within
+Rcpp Modules \citep{CRAN:Rcpp:Modules}.  Some more background on the linking
+requirement is [in this SO
+question](https://stackoverflow.com/questions/2424836/exceptions-are-not-caught-in-gcc-program).
+