[Rcpp-devel] assert() for Rcpp?

JJ Allaire jj.allaire at gmail.com
Wed Feb 18 01:53:27 CET 2015

I agree that having an assert which complies with CRAN standards would
be valuable.

One piece of immediate feedback on your initial implementation: you
can't call Rf_error from C++ code (as it will bypass C++ destructors
on the stack). Rather, you should throw Rcpp::exception.

Whether assert should throw is another issue entirely. The traditional
semantics of assert don't give it control flow behavior (either do
nothing in release mode or blow the process up in debug mode) so I'm
not sure whether we'd want to introduce a variation of it that does
have control flow. A couple of options:

(1) Create another function e.g. "verify" with the semantics you
suggest (with the different name not fooling people into thinking it
has traditional assert semantics)

(2) Call it assert but have it call Rcpp::warning rather than yielding an error.

On Tue, Feb 17, 2015 at 5:41 PM, Miratrix, Luke
<lmiratrix at fas.harvard.edu> wrote:
> Dirk Eddelbuettel and I were discussing how people do not seem to be
> putting assert() statements in their C code in Rcpp packages.  I expect
> the reason is because assert() prints to cerr, which is a violation of the
> CRAN policies of proper packages.  However, the assert() command is a
> simple macro, and we could tweak it so it is compliant with CRAN
> standards.  Below, I have an example of what might be included.  Dirk
> suggested that this idea be posted to this list to gather peoples insights
> and thoughts (and to catch any memory management issues, for example, that
> might exist with the code below).
> The traditional assert() is a macro that calls a function __assert() which
> in turn seems fairly simple, but the C program for Rcpp should not just
> abort but instead throw an error, I think.  (The macro allows for
> detection of line numbers in the code, and also allows for a NDEBUG flag
> to omit all asserts for efficient code.)
> The proposed code:
> #include <stdio.h>
> #ifdef NDEBUG
> # define assert(EX)
> #else
> # define assert(EX) (void)((EX) || (__assert (#EX, __FILE__, __LINE__),0))
> #endif
> void __assert (const char *msg, const char *file, int line) {
>     char buffer [100];
>     snprintf( buffer, 100, "Assert Failure: %s at %s line #%d", msg, file,
> line );
>     ::Rf_error( buffer );
> }
> Anyway, I would love to hear people¹s thoughts on this.  I found assert()
> useful in wrapping an existing spaghetti code base with an R package; it
> seems like a nice tool to provide enhanced ability to track down bugs.  I
> am currently using the above in my package Œtextreg¹ and it appears to
> work great.
> Sincerely,
> Luke Miratrix
> Assistant Professor of Statistics
>         Note: Due to my RSI (wrist trouble), e-mail often abrupt.
> --
> Department of Statistics
> Science Center
> Harvard University
> 1 Oxford Street
> Cambridge MA 02138-2901
> lmiratrix at stat.harvard.edu
> 510-735-7635
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