From: Timothy Hunter <cyclists@...>
Date: 2005-12-06T11:17:34+09:00
Subject: Re: Overloaded constructors in Ruby

Kyle Heon wrote:
> I think I understand the error, it's expecting 5 arguments (based on the
> last constructor) but I don't the "Ruby" way to set this up. What am I
> missing?
> 
> I was able to get this to work, but was hoping that I could do it in a
> format closer to the above to make it a little more flexible to use.
> 
> class GravPoint
>     def initialize(x = 0, y = 0, strength = 0, ctime = 0, life = 0 )
>         @x, @y, @strength, @ctime, @life = x, y, strength, ctime, life
>     end
> end

Actually, defining default values for arguments is a very "Ruby" way of 
handling this case. If the arguments have sensible default values, then 
I'd argue that it's the best solution. You could also use a hash to 
simulate named parameters if that's what floats your boat. Another very 
"Ruby" thing to do is to define multiple constructors with different names.

Something I've done is to define a "basic" constructor and then define 
one or more methods that modify the basic instance. For example, suppose 
you have two kinds of rectangles, a regular square-cornered rectangle 
and a rectangle with rounded corners. The difference between the two 
rectangles is that the rounded rectangle needs an extra 2 numbers to 
define the radii of the ovals that make up the corner. If you want a 
plain rectangle just call "new". If you want a rounded rectangle, modify 
the newly-constructed instance by calling "rounded" on it.

class Rectangle
    def initialize(width, height)
       @width, @height = width, height
    end

    def rounded(rx, ry)
       @rx, @ry = rx, ry
    end
end

rect = Rectangle.new(20, 30)
round_rect = Rectangle.new(20, 30).rounded(2, 3)