Dear GAP Forum, Yevgen Muntyan's post and the discussion which follows raise the question of managing the global variable namespace as the number of packages in GAP grows.
Some guidelines in this direction appear on the Web site at http://www.gap-system.org/Packages/Authors/variablenames.html. To answer specifically Yevgen's question: > Should packages use operations as much as possible? the answer, as explained on that page is "basically yes". Indeed, where appropriate, Attributes should even be preferred to Operations. In the ensuing discussion, there was some concern about performance costs of method selection. As someone else pointed out, this is very small. On my laptop (Pentium M 2.1 GHz) the cost of calling a one argument function that does nothing as a method of an operation is about 20ns more than calling it directly (about 100ns per call, vs about 80). Admittedly this is the ideal situation (since there are no other methods or calls to this operation, my method is sure to be first in the cache), but real life should get pretty close to this. GAP caches the last few sets of argument types with which an operation has been called and checks them first. Almost all operation calls are cache hits. Unless you have very clear evidence that it is a problem then, I would suggest that programming around the method selection system is likely to complicate your code without gaining you much performance. It can be helpful to also store your methods in global functions for debugging or profiling purposes, but in this case you should certainly either (a) use "non-obvious" names, or (b) remove these assignments from the released version of your package. I should say that there is one awkward exception to this generally good performance, namely when one of the arguments is a plain list with mutable entries. In this case determining its type must be repeated at every operation call, and can be expensive. We have some longer term plans to address this, but thy will involve significant changes and will take a while to work through. We have discussed the idea of introducing some version of namespaces into GAP, but nothing is currently planned. Steve Linton -- Steve Linton School of Computer Science & Centre for Interdisciplinary Research in Computational Algebra University of St Andrews Tel +44 (1334) 463269 http://www.cs.st-and.ac.uk/~sal Fax +44 (1334) 463278 _______________________________________________ Forum mailing list Forum@mail.gap-system.org http://mail.gap-system.org/mailman/listinfo/forum
