From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2009-01-12T18:07:29+09:00
Subject: Re: Dynamically created attributes

On Mon, Jan 12, 2009 at 10:03 AM, Jesús Gabriel y Galán
<jgabrielygalan@gmail.com> wrote:
> On Mon, Jan 12, 2009 at 9:25 AM, Peter Marks <petertmarks@gmail.com> wrote:
>> I'd like to specify a quantity of object attributes when creating an
>> instance of an object. For example, I would like to create a Grid object
>> with 4 different 'row' attributes like this: Grid.new(4). Here's some
>> dirty code that does that:
>>
>> class Grid
>>  #Creates row1, row2, etc. depending on row arg
>>  def initialize(rows)
>>    row_count = 1
>>    rows.times do
>>      instance_eval "@row#{row_count} = 'xxx'"
>>      row_count += 1
>>    end
>>  end
>> end
>>
>> It's dirty, but it creates the attributes. I don't see how to
>> dynamically create accessor methods for all these attributes though. Any
>> suggestions? I sense there's a better way to do this.
>> --
>> Posted via http://www.ruby-forum.com/.
>>
>>
>
> Maybe this is cleaner:
>
> class Object
>        def singleton_class
>                class << self; self; end
>        end
> end
>
> class Grid
>        def initialize rows=0
>                rows.times do |i|
>                        instance_variable_set "@row#{i}", "initial value"
>                        singleton_class.instance_eval {attr_accessor "row#{i}"}
>                end
>        end
> end
>
> irb(main):020:0> a = Grid.new 3
> => #<Grid:0xb7c02008 @row0="initial value", @row2="initial value",
> @row1="initial value">
> irb(main):021:0> a.methods.grep /row/
> => ["row0", "row0=", "row1", "row1=", "row2", "row2="]

Ooops, my solution starts with 0, while you wanted to start with 1.
Anyway, an easy change. Nevertheless, I agree with Stefano that this
would be better off implemented as an array, instead of having
individual variables for each "field".

Jesus.