How to have contract for your parameter object?

Question

Say you have type(interface/class) A and A has

A.setX(String x) (and all gets)
A.setY(String y)
.
.

And you have this API:

save(A a);

save method requires A to have X, Y and 10 other values set, but a few other properties are optional. So how can save method tell this kind of requirement to rest of the world?

You can assume that the caller only knows about the signature and documentation of method.

Answer 1

Depending on what your application is, you might want to consider making A an immutable type that had to have x and y set at all times. Then, the save method will always work.

Failing that you could give the save method the appropriate preconditions (possibly implemented with assertions if your language supports them and they're appropriate for your application).