From: Joel VanderWerf <vjoel@...>
Date: 2008-04-21T07:12:28+09:00
Subject: Re: A couple of questions regarding class design

Michael W. Ryder wrote:
> I am part way through implementing a Rational math class to further my 
> understanding of Ruby and had a couple of questions that I can't find 
> the answer to in Pickaxe.
> The first question regards creating a new instance of the class.  The 
> initialize method expects two integer values.  While I have no problem 
> making sure that they are integers I am not sure what to do if they are 
> not.  Do I return nil or some other result?

You could raise an exception:

unless ...
   raise ArgumentError, "Rational arguments must be integers"
end

> The other question is how to override basic math operations like 
> addition and multiplication.  I could implement them as x.add(y) but 
> would prefer to just be able to enter x + y.  I think I have to create a 

class Myclass
   def +(x)
     ...
   end
end

> new instance of the class for the result and return that but am not sure 
> how to make it so that Ruby calls the right method when it sees x + y.
> On a related note is there any good source for writing operations like 
> the math and probably coerce?  If I can get the math working the 
> comparable operations should be "trivial".

There's some explanation of how to write coerce methods in the PickAxe 
(p. 358 of my 2nd ed. pdf copy).

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407