From: "Ara.T.Howard" <Ara.T.Howard@...>
Date: 2005-09-15T12:21:35+09:00
Subject: Re: params v.s. @params in rails?

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On Thu, 15 Sep 2005, Ron Jeffries wrote:

> On Mon, 5 Sep 2005 01:26:44 +0900, David Heinemeier Hansson
> <david.heinemeier@gmail.com> wrote:
>
>>> The recommendation for using the params method, instead of accessing
>>> the @params instance variable directly, is that it=B4s more uniform to
>>> use the accessor method, since you can also do that from the view.
>>
>> Direct access to these instance variables is deprecated. The same goes
>> for cookies, session, request, response, and the other accessors. Use
>> the accessor instead of going directly, so it's request.get? instead
>> of @request.get?.
>
> David, Chet Hendrickson and I are just getting back to Ruby after too lon=
g away,
> and we've just started working through the Rails book. Mostly happy so fa=
r,
> though we're just a couple of days in.
>
> One thing that confused me was the validate method in the first example. =
I'm
> sure I'm missing something really obvious, but I'd rather be embarrassed =
than
> confused. ;-> The validate is:
>
>  def validate
>    errors.add(:price, "should be positive") unless price.nil? || price >=
=3D 0
>  end
>
> I don't see how "price" canrefer to the field in the record, unless price
> isperhaps an accessor kind of method. But in the class definition, I don'=
t see
> any declaration of a price method.

runtime and compile time aren't that different in ruby:

   harp:~ > cat a.rb
   class Row < ::Array
     FIELDS =3D %w( product price )

     def method_missing(m, *a, &b)
       idx =3D FIELDS.index m.to_s
       return self[idx] if idx
       super
     end
   end

   row =3D Row[ 'foobar', '17 bucks' ]

   p row.price

   harp:~ > ruby a.rb
   "17 bucks"


this routes through method_missing each time, which is expensive, but you c=
an
define the method at that point so future calls don't:

   harp:~ > cat a.rb
   class Row < ::Array
     FIELDS =3D %w( product price )

     def method_missing(m, *a, &b)
       idx =3D FIELDS.index m.to_s
       if idx
puts 'defining the method once...'
         self::class.class_eval <<-definition
           def #{ m }
             self[ #{ idx } ]
           end
         definition
         send m
       else
         super
       end
     end
   end

   row =3D Row[ 'foobar', '17 bucks' ]

   2.times{ p row.price }


   harp:~ > ruby a.rb
   defining the method once...
   "17 bucks"
   "17 bucks"


it's precisely these sorts of possibilties which makes ruby such an attract=
ive
means of writing code with dynamic responsibilies and requirements..

cheers.

-a
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| email :: ara [dot] t [dot] howard [at] noaa [dot] gov
| phone :: 303.497.6469
| Your life dwells amoung the causes of death
| Like a lamp standing in a strong breeze.  --Nagarjuna
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