Re: dynamic assignment of instance variables

On Thu, 4 Mar 2004 10:02:44 +0100, "Robert Klemme" <[e-mail]> wrote:
>I think that there is a subtle difference between "instance variables" and
>"attributes": an instance variable is a "physical thing", i.e., an
>instance does in fact have a variable defined that carries a value.  An
>attribute OTOH is something seen from the outside that does not
>necessarily relate to an instance variable, although attr, attr_accessor
>and the like tend to make people think they are tied together.  It's
>perfectly legal to have an attribute that has no 1:1 relationship with an
>instance variable.

I agree.  This should be basic Ruby (and perhaps basic OO).

>Apart from that someone might have redefined attr, attr_accessor etc. to
>generate other methods than the default methods...

That would be no problem I think, because this redefinition would be reflected
in the accessors themselves, i.e., the behaviour of the accessors would
change along.

It's just that I am too lazy to write the method "attribute_set"
myself AND that this method seems standard enough to be expected as
Ruby built-in method.

Or does my requirement clash with obvious Ruby or OO philosophy?
Please let me know.  Thanks.

sh-2.04$ cat try_accessors.rb
class Object

   def attribute_set(k, v) # should be built-in
      send "#{k}=", v # interpolation, yuck
   end

end

class Person

   attr_accessor :name, :born

   def initialize(args)
      args.each do |attr,val|
         attribute_set(attr, val) # should raise an error if attr's are not settable
      end
   end

end

p Person.new(:name => 'John', :born => '2003')

sh-2.04$ ./try_accessors.rb
#<Person:0x2a876d8 @born="2003", @name="John">
sh-2.04$ _