[Python-Dev] Finalization in Eiffel (original) (raw)

Tim Peters tim_one@email.msn.com
Fri, 10 Mar 2000 21:03:47 -0500

Eiffel is Bertrand Meyer's "design by contract" OO language. Meyer took extreme care in its design, and has written extensively and articulately about the design -- agree with him or not, he's always worth reading!

I used Eiffel briefly a few years ago, just out of curiosity. I didn't recall even bumping into a notion of destructors. Turns out it does have them, but they're appallingly (whether relative to Eiffel's usual clarity, or even relative to C++'s usual lack thereof <0.9 wink>) ill-specified.

An Eiffel class can register a destructor by inheriting from the system MEMORY class and overriding the latter's "dispose()". This appears to be viewed as a low-level facility, and neither OOSC (2nd ed) nor "Eiffel: The Language" say much about its semantics. Within dispose, you're explicitly discouraged from invoking methods on any other object, and resurrection is right out the window. But the language doesn't appear to check for any of that, which is extremely un-Eiffel-like. Many msgs on comp.lang.eiffel from people who should know suggest that all but one Eiffel implementation pay no attention at all to reachability during gc, and that none support resurrection. If you need ordering during finalization, the advice is to write that part in C/C++. Violations of the vague rules appear to lead to random system damage(!).

Looking at various Eiffel pkgs on the web, the sole use of dispose was in one-line bodies that released external resources (like memory & db connections) via calling an external C/C++ function.

jealous-&-appalled-at-the-same-time-ly y'rs - tim