> Hi Arran,

> I've approached this question differently. For ISP I'm applying it to the fields of the objects and not the objects themselves, e.g. Instead of partitioning Location, I'm partitioning the name of Location.

In cases where a class consists of "plain old data" – i.e., the class doesn't do any significant abstraction or information hiding – then partitioning up a parameter of that class will amount to pretty much the same thing as partitioning up its fields. If the class does do information hiding or has invariants, then the domain might be smaller (and we might not have access to the fields at all).

Let's look at some concrete examples. If some method takes a primitive type as parameter (e.g. an int), then things seem straightforward – we partition up the range of possible ints. If the method specifically excludes some values as being undefined (maybe 0 is never allowed to be passed), then that makes our domain smaller.

If we have a class which basically is just a wrapper around, say, 3 ints, then we can partition objects of that class just by partitioning the individual ints.

But suppose we have a Date class, with year, month and day probably implemented as ints, but which are only exposed via "getter" methods (and which are presumably constrained by class invariants). A Date class presumably constrains the month to be in the range 1-12, and the day to be a valid day for the month. In that case, we don't have direct access to the field anyway, so it doesn't really make sense to talk about partitioning them, and even if we did, many of the possible int values are ruled out by the class specification. It would make more sense to partition the class based on properties like: is this the first or last month of the year? Is the year positive, 0 or negative? (We're unlikely to schedule meetings for 10 BCE, but I suppose historians might like to accurately model such dates.) Is the day the first or last day of the month? (And if we are testing a constructor which promises to throw exceptions when an invalid day is supplied, our partitions would include invalid days as well - but those would be partitions used for testing the constructor of class Date, not partitions for methods that use class Date or take it as a parameter.)

Does that assist at all?

cheers

Arran