[gmx-developers] Trade-offs between encapsulation and low level modifications of class variables.

[David van der Spoel]

Hi,

recently (over the last year) I have been working on the electric field 
code as a template for other applied forces. Teemu has done tons of work 
commenting, cleaning up and adding more patches with the result that we 
now almost have a complete framework for reading e.g. MDP and TPX files 
with the same code (correct me if I'm wrong), and a JSON mdp file should 
be doable in the near future as well.

In the process lots of encapsulation has been done of the type "bare 
outside class interface with Impl_ for the details". Obviously this has 
many advantages like decluttered interfaces and modularization.

However, part of the rationale for my changes was to be able to modify 
e.g. the electric field parameters from a program (not mdrun) and 
re-evaluate the energy and dipole of a molecule, which would yield the 
polarizability. The functions to do this are now not accessible anymore, 
except by faking reading a new MDP input, and even that is not possible 
anymore outside readir.cpp since the last few patches (most of which I 
approved :) ).

There may be similar cases, where one would like to change variables, 
like steered MD, certain free energy schemes or analysis tools. I'm a 
bit at a loss how to deal with this, would be great to have some 
feedback on this.
-- 
David van der Spoel, Ph.D., Professor of Biology
Dept. of Cell & Molec. Biol., Uppsala University.
Box 596, 75124 Uppsala, Sweden. Phone:	+46184714205.
spoel at xray.bmc.uu.se    http://folding.bmc.uu.se