From: dblack@...
Date: 2007-08-02T23:18:48+09:00
Subject: Re: Beginner's tutorial and poor attempt at classes

Hi --

On Thu, 2 Aug 2007, Gabriel Dragffy wrote:

> Hi all
>
> I just started with Ruby (yesterday actually). Have been reading the amazing 
> Poignant Guide, and also a couple of other very basic tutorials. From one of 
> these I wrote an example class, now my knowledge of Ruby has expanded a 
> little I tried to rewrite the class to be even better.  I thought that the 
> method "setme" would allow the @numberShowing to be changed to any number 
> between 1 and 6... but obviously not...?
>
>
> #/usr/bin/env ruby
>
> class Die
> def initialize
>   roll
> end
>
> def roll
>   @numberShowing = 1 + rand(6)
> end
>  def showing
>   @numberShowing
> end
>
> def setme value
>      if value === 1..6
>     @numberShowing = value
>   else
>     puts "A dice has only six sides!"
>   end
> end
>
> end

You've got the === backwards; you want:

   if (1..6) === value

or

   if (1..6).include?(value)

Here's a little rewrite, using a reader attribute to streamline the
retrieval of the die's number:

class Die
   attr_reader :number

   def initialize
     roll
   end

   def roll
     self.number = rand(6) + 1
   end

   def number=(value)
     if (1..6).include?(value)
       @number = value
     else
       puts "A die has only six sides!"
     end
   end
end

With this, you can do things like:

die = Die.new
puts die.number
die.roll
puts die.number
die.number = 20    # A die has only six sides!

You could also make the number= method private, to discourage (though
not entirely prevent, since private doesn't do that) people from
setting the number manually.


David

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