Question

I have to implement Java.Polynomial as a school assignment. Part of the methods are add(polynomial), multiply(polynomial) etc.

In the case of something like

p.add(q); // computes p + q 

is it better to return void and keep the sum of the polynomials in p? or is it better to return a polynomial and keep the former value of p intact?

My instinct tells me that i should do the following

• implement p.add(q) as a ‘destructive’ method… it adds q to the value of p and stores the sum in p
• also implement a static method Polynomial.add(p,q) which returns the sum of the polynomials.

What do you think?

Answer 1

Personally I really like immutable types. I would write p.plus(q) instead of p.add(q) and make it return a new polynomial. Immutability has a lot going for it, not just in terms of thread-safety (which sounds like it won’t be an issue in this case) but also in terms of reasoning about your code. It’s a lot easier to predict what’s going to happen if you know that nothing can change the contents of an object under your feet once you’ve stashed a reference to it.