>> Every module is indepently tested and proven to work as designed. Most
>> of the problems I run into are related to bad data.
>
>you mean, as in, the module did not defend against (check for) bad data ?
>is data validation specified as part of your module specifications ?
>or do you just rely on field validation at input time ?

Had a thought on this that I want to share. Beginning with VFP 6.0, validating data for objects became a whole lot easier with the _Access and _Assign events. Combined with the bitwise functions, it makes checking for a large number of properties a snap. The following is from my own work.

I had a situation where a large number of properties (over 20) had to be properly initialized prior to making some very complex calculations. By adding an _Assign method to each property, I was easily able to validate the incoming information. If the information was valid, I set a bit of an integer property to indicate that the data was valid. If it was invalid, I made sure that the bit was cleared. Each property was thus represented by a bit. Using BITAND() allowed me to easily test to make sure that all the necessary properties were properly initialized.