From: Sean O'Halpin <sean.ohalpin@...>
Date: 2008-05-11T03:29:58+09:00
Subject: Re: Reading from file, create a class with variables

On Sat, May 10, 2008 at 5:44 PM, ara.t.howard <ara.t.howard@gmail.com> wrote:
> class Specd
>  alias_method '__eval__', 'instance_eval'
>
>  instance_methods.each{|m| undef_method m unless m[%r/__/]}

D'oh! Overlooked the obvious.

>
> the point of blowing away all the methods in spec'd is so i can intercept
> any DSL-ish methods and apply them to the class i'm building.  using this
> sort of DSL wrapper allows me to build up a class with a dsl without
> littering the class itself with useless DSL crap.

Namespaced methods would help. Agreed about littering - I'm currently
refactoring doodle to be as unobtrusive as possible.

>
>  class Model
>
>     has_many :foos
>
>   end
>
> relies on Model having a has_many method.  this is sometimes not desirable
> as it may require, for instance, inheriting from some abstract base type.
>  with the 'dsl as wrapper approach' one can do
>
>  Model = DSL.build do
>
>     has_many :foos
>
>  end
>
> and Model can be a totally 'normal' class - all the special DSL-y goodness
> on how to build up stuff is contained in the DSL object, which has a @model
> instance and all methods stripped except the dsl ones.

You could also have

  DSL(Model) do
    has_many :foos
  end

or the like to decorate existing classes. I'm using a similar approach
in one of my 'least footprint' experimental versions of doodle.
In miniature, something like this:

class ClassExtensions
  attr_accessor :model
  def initialize(model, &block)
    @model = model
  end
  # DSL method
  def has(*args)
    model.class_eval { attr_accessor(*args) }
  end
end

def DSL(klass, &block)
  ce = ClassExtensions.new(klass)
  ce.instance_eval(&block)
end

class Foo
end

DSL(Foo) do
  has :name
end

foo = Foo.new
foo.name = 'Trillian'
foo.name # => "Trillian"
p Foo.methods - Object.methods
# >> []

which is basically the same approach as yours I believe.

> this code works very similarly
>
>  http://codeforpeople.com/lib/ruby/configuration/configuration-0.0.5/lib/configuration.rb
>

Yup, and very instructive it is too :)

Regards,
Sean