From: "F. Senault" <fred@...>
Date: 2008-03-16T05:34:55+09:00
Subject: Re: How to iterate through instance attribute names (attr_accessor)

Le 15 mars 2008 � 20:21, Stefano Crocco a �crit :

> Of course, you can also keep an array of the names of those instance variables 
> for which a validation method exists and use the following code:
> 
> def validate
>   [:a, :b, :c, :d].each{|v| send "validate_#{v}"}
> end

You can metaprogram your way around it too.  Full example (that can
surely be improved) :

module Kernel
  def attr_with_validation(*atts)
    unless method_defined? :validate
      class_eval <<-_EOE
        @_validations = []
        def self.validations
          @_validations
        end
        def validate
          self.class.validations.each do |v|
            self.send("validate_\#{v}")
          end
        end
      _EOE
    end
    atts.each do |att|
      class_eval <<-_EOE
        @_validations << :#{att}
        def #{att}
          @#{att}
        end
        def #{att}=(v)
          @#{att} = v
        end
      _EOE
    end
  end
end

class Toto
  attr_with_validation :a, :b
  attr_with_validation :c

  def validate_a() ; raise if @a.nil? ; end
  def validate_b() ; raise if @b.nil? ; end
  def validate_c() ; raise if @c.nil? ; end

  def initialize(a)
    @a = a
  end
end

t = Toto.new("I'm a")
t.b = "Hoy b"

puts t.a
puts t.b

t.validate

Result is :

I'm a
Hoy b
./validate.rb:38:in `validate_c': unhandled exception
        from (eval):7:in `send'
        from (eval):7:in `validate'
        from (eval):6:in `each'
        from (eval):6:in `validate'
        from ./validate.rb:51