Lua 5.3 and C++ exceptions

[Colin <lua@...>]

Hi,

following the announcement of Lua 5.3 with the greatly appreciated addition of native integer support we are planning to update a bunch of C++ projects from Lua 5.1 and were wondering how the compatibility with C++ exceptions has progressed.


The scenario that we are looking at is

C++ application
calls
Lua function
calls
C++ function

when the inner C++ function throws an exception.


Currently we handle this situation at the Lua-to-C++ call point by wrapping the C++ function in a try-catch block that logs an exception and calls the Lua error function; at the C++-to-Lua transition we detect the Lua error and then throw a C++ exception.

(With C++11 we could improve this approach by extending the Lua state by a std::exception_ptr, storing the exception caught at the Lua-to-C++ transition there, and re-throwing it at the C++-to-Lua point.)


The question is, can this be simplified?

Ideally the C++ exception would simply “fly through” the Lua interpreter from the inner C++ function to the outside C++ application, but as far as I understand, that is not, or at least: was not possible because Lua obviously can’t use RAII and requires an explicit call to its error handling facilities to keep everything consistent.

If this “flying through” does not work unmodified, is it possible to somehow “patch up” things, i.e. let the exception fly through and then afterwards, in a try-catch at the C++-to-Lua point, call some Lua function to put things back into a consistent state? (This would allow leaving out the try-catch around the inner C++ function and not require adding the exception_ptr to the Lua state to recover the original exception.)

Or what else is the recommended way of handling this interoperability question, what is the current “best practice”?

Thanks, Colin