[cppx] Exception translation, part II

In part I I showed how to use the cppx library’s exception translation support, which decouples the specification of how non-standard exceptions should be translated, from each routine’s invocation of such translation. The translation can be customized by dynamically installing and uninstalling exception translator routines. And essentially each routine that wants exception translation must use a catch (this will most often be a generic catch(...)) where it invokes cppx::rethrowAsStdX, which in turn invokes the installed exception translator routines and performs a default translation if none of them apply.

In this second part I discuss how that translation machinery works.

In part III I’ll discuss the support for installation and uninstallation of exception translator routines. And perhaps I’ll need a part IV to discuss the cppx exception types! Anyway, now, diving down into the code…

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[cppx] Exception translation, part I

MFC throws pointers, Xerces throws various types not derived from std::exception, and as I recall the Lotus Notes API throws integers. An interesting diversity. But as the Chinese curse goes: may you live in interesting times! Such non-standard exceptions generally require you to have multiple catches every place such an exception could otherwise escape to higher levels, or where you want to handle any exception with a given general meaning. It’s not that the designers have tried to be clever or that they’re out to get you: it’s just that these libraries stem from before C++ was standardized, i.e., before 1998.

One partial remedy is exception translation. Somehow arrange for any non-standard exception to be caught and result in some corresponding exception derived from std::exception. It does not solve all the problems – but it sure beats doing it by copy-n’-paste coding of exception handlers!

With C++98 exception translation cannot be completely centralized in a portable, reusable way. As far as I know that’s not possible even with the upcoming C++0x standard. But it’s possible to provide portable and application-independent support that does most of the job, and that provides a general convention that largely eliminates the chance of any non-standard exception slipping through, and that’s what I discuss here.