From: Dennis Ranke <dennis.ranke@...>
Date: 2004-08-04T21:21:30+09:00
Subject: Re: Macros in Ruby

On Wed, 4 Aug 2004 09:12:41 +0900, Joel VanderWerf  
<vjoel@PATH.Berkeley.EDU> wrote:

> Jesse Jones wrote:
>> For example, suppose you're writing a game and you have a lot of code
>> that selects behavior based on percentages (75% of hits are normal
>> blows, 20% are critical hits, and 5% kill your foe out-right for
>> example). Even in a language as expressive as Ruby this is a bit
>> awkward to write and not especially intentional. But with macros it can
>> be written very cleanly:
>>  percent-case
>>    0.75 case
>>       normal_hit
>>    end
>>     0.20 case
>>       critical_hit
>>    end
>>     otherwise
>>       kill_foe
>>    end
>> end
>
> It's not really that hard to do something like this in ruby, but it is a  
> little less efficient than it would be with macros.
>
> [...]

Or you could even do it like this, which looks (to me) even nicer than the  
macro solution :)

class PercentCase
   def initialize
     @v = rand(100)
   end
	
   def test(o)
     @v -= o
     @v <= 0
   end
end

class Integer
   alias_method :percentCase, :===
   def ===(o)
     if o.is_a? PercentCase
       o.test self
     else
       percentCase o
     end
   end
end

10.times do
   case PercentCase.new
   when 75
     puts 'normal_hit'
   when 20
     puts 'critical_hit'
   else
     puts 'kill_foe'
   end
end

-- 
exoticorn/farbrausch