[Cuis-dev] Possible improvements for method lookup simulation

[Facundo Javier Gelatti]

Hello!

I've been experimenting with some improvements for the messages we use to
simulate the method lookup (i.e. Behavior>>#lookupSelector:), motivated by
the OOP courses I teach (where I like to show the implementation of the
method lookup). I figured the changes might be of interest for integration
on the Cuis base image, so I'm sending some proposals!

The changes I propose are twofold:
1. Change sets 1-2x are a proposal to have a new #lookupSelector:ifAbsent:
message, to be able to specify what to do when the selector is not found
(instead of always returning nil). The change set labelled 1 introduces it,
and the ones labelled as 2x use it in some of the methods we already have.
I tried to name the files as descriptively as possible, to help during
review.
2. Change set 3 is a proposal for a new implementation of
#lookupSelector:ifAbsent:. The implementation I propose avoids using a
while loop, it's a recursive implementation which I find a bit less
imperative (and, might I say, "more object-oriented"). Surprisingly, the
implementation has also better performance compared with the current one
(it runs about 30% faster)¹.

To be able to evaluate the second proposal, I attach some useful scripts:
* Some benchmarks for the average case and two "worst cases".
* A (partial) correctness test, which asserts that the methods found by
both implementations are the same (traversing all the methods in the image).
* A script to try it out with very deep class hierarchies.
These scripts should be evaluated manually in a workspace, while switching
between the two implementations.

I hope you find these changes, if not useful, at least interesting!
Cheers!
Facu

______
¹ Of course, being a recursive implementation, it limits the class
hierarchy depth by the stack size. But since the depth of all inheritance
hierarchies on the image is less than 20, and having a deep inheritance
hierarchy is already a design smell, we might consider taking the design +
performance improvement. Also, currently the maximum stack size is limited
by RAM (at least by default), so the change works with very large
hierarchies too (see the attached very_deep_hierarchy_test.st script).
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