Re: concerns when integrating C++ code into guile?

[Chris Vine]

On Tue, 06 Jan 2015 18:32:10 -0800
Matt Wette <address@hidden> wrote:
> What are the concerns when integrating C++ code into guile?
> 
> I'm guessing interleaved C++ exception handling, but are there others.
> 
> Assuming the C++ code calls no guile code, should all C++ exceptions
> be caught at the interface?

Things come in clumps, as there was a thread about this a few days
ago.  If your question could be re-expressed as "what are the concerns
when calling libguile in C++ code", then the rules I follow do indeed
mainly relate to exception handling, and are:

1.  Don't allow a guile exception to take a C++ object with a
non-trivial destructor out of scope.  (Compare §18.10/4 of C++11: "A
setjmp/longjmp call pair has undefined behavior if replacing the setjmp
and longjmp by catch and throw would invoke any non-trivial destructors
for any automatic objects.")  Bear in mind also that most libguile
functions can throw a guile exception, if only an out-of-memory
exception, but there are many others - type mismatches and so forth.

2.  Don't allow a C++ exception to propagate out of a guile dynwind
block, nor out of a function with C language linkage.  (Someone has
suggested that you could propagate a C++ exception out of a function
with C language linkage if the C code has been compiled with gcc using
its -fexception language extension, but that still might not get you
very far in practice.)

3.  If you are passing a user function (via a function pointer) to
libguile, give it C language linkage, although gcc and clang are
forgiving about this as they use the same calling convention for C
functions, C++ non-member functions and C++ static member functions
(but the standard does not mandate that).

There are other issues to consider if you intend to call libguile in
your program in more than one thread.

This may, or may not, give you some ideas:
http://sourceforge.net/p/cxx-gtk-utils/git/ci/master/tree/c++-gtk-utils/extension.h

Chris