Configuration Conventions

For non-programmers, MATSim is configured via the config file.
(For extensions, we have not yet found a good solution.)
If you make your code configurable, please observe the following hints.

Avoid automagic

Examples for automagic are:

• If the code finds a file of a certain type, then do something special.
• If the code finds a config module of a certain type, then do something special.
• If some values are overwritten then some other values are cleared.

The problem with such automagic is that it is nearly impossible to write code that is robust against typoes. As a result, one gets warnings such as

• “File of certain type not found, thus assuming …” (This may either be a deliberate user decision, or a typo on the filename.)
• “Config module of a certain type not found, thus assuming …” (This may either be a deliberate user decision, or a type in the module name.)
• “Config module of a certain type found, thus assuming …” (This may be a leftover module from some other experiments.)
• “When you are overwriting value X please remember that this also affects values Y and Z.” (Which may be what the user wants, or not.)

If a user is not able to switch off warnings, she or he will eventually start to ignore them. Which is not good. In that sense:

Avoid warnings that cannot be switched off

If a user is not able to switch off warnings, she or he will eventually start to ignore them. Two aspects:

• Automagic should be avoided (see above).
• If the user is doing something non-standard/not-recommended, this may lead to a warning. It would make sense to provide a switch to disable such warnings. (Makes the configuration file a lot longer, though.)