On Tuesday, 8 April 2014 at 10:08:24 UTC, Jacob Carlborg wrote:
Is there a reason to not use the same model, or what's required to be compatible?
In short, the reason not to use the same "model" (you could argue that the model is the same, as only the personality functions differ) is that the exception unwinder is intimately tied to both the target language ABI and semantics.
For example, all unwinders need to handle the run-time type information for the exception object to correctly dispatch it. And while e.g. the GNU C++ unwinding implementation needs to pull shenanigans to implement the crazy C++ exception lifetime model (cf. catching by reference vs. by value) and enforce throws(...) specifications, the D unwinder needs to understand the difference between Exception and Error and correctly implement exception chaining.
Now, of course, it is possible to find a middle ground that works as a basis for virtually all languages. In fact, I'd argue that SEH for Windows actually provides such a layer, and libunwind does too. For example, a proper implementation of a libunwind personality function allows you to check whether a given exception originated in your own language, and just pass it on otherwise (such that e.g. C++ exception just bubble through a layer of D code). In theory, it would e.g. also be possible to wrap foreign exceptions in e.g. D Throwable objects to make them catchable in D code. But the lifetime of the foreign object is virtually impossible to get right in the general case, and the benefits of wrapping exceptions like this have turned out not to be worth it, because it is hard to handle them in a sensible way in the receiving language (DMD actually does – did? – something like this on Win32).
David
