From: James Edward Gray II <james@...>
Date: 2010-11-03T03:12:02+09:00
Subject: Re: the dark side of inherited methods

On Nov 2, 2010, at 1:04 PM, Joel VanderWerf wrote:

> On 11/02/2010 10:02 AM, Josh Cheek wrote:
>> On Tue, Nov 2, 2010 at 11:19 AM, James Edward Gray II<james@graysoftinc.com
>>> wrote:
>> 
>>> Of course, inheritance has it's place and uses but I feel it's definitely
>>> overused.
>>> 
>>> 
>> Can you give some examples of where it has its place? I have been trying to
>> think of one, and can't. I realized the only time I ever subclass anything
>> is ActiveRecord::Base (and I'm not really sure what that offers over
>> modules, DataMapper uses modules, for example).
> 
> The shortest example that occurs to me:
> 
> class A < Struct.new :x, :y, :z
>  def length
>    Math.sqrt(x**2 + y**2 + z**2)
>  end
> end
> 
> That only saves a couple of keystrokes compared to:
> 
> A = Struct.new :x, :y, :z
> class A
> ...
> 
> but it's cleaner IMO. Also, it allows you to do this:
> 
>  def x=(new_x)
>    raise ArgumentError if new_x > 100
>    super
>  end
> 
> In the "A=Struct.new" approach, you have to muck around with alias to get the same effect.

Neither are required though, since Struct.new() takes a block:

  A = Struct.new(:x, :y, :z) do
    def length
      Math.sqrt(x**2 + y**2 + z**2)
    end
  end

James Edward Gray II