From: John Lam <drjflam@...>
Date: 2006-05-04T22:35:26+09:00
Subject: Re: Ruby idiom for attributes / properties

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Hi Dave,

Duck typing for attributes - cool idea, but I worry about it because of the
difficulty (impossibility) in telling read-only properties from ordinary
methods:

module Utilities
  def format_disk
  end
end

class Person
  include Utilities
  def first_name
  end
end

You see my interest in this topic is driven entirely around my ability to
add some runtime magic in my marshaler. Since the metadata doesn't exist in
Ruby, I have to rely on some kind of convention. I might need to add that
convention via a mixin that you can write that serves as an adapter between
the type that you want to make data-bindable in .NET. So you could patch
ActiveRecord in a RubyCLR app via:

class ActiveRecord
  include RubyClr::MakeBindable
end

This removes the hard-coded depenency on ActiveRecord from my marshaler.

Does this sound reasonable?

Thanks
-John
http://www.iunknown.com



On 5/4/06, Dave Burt <dave@burt.id.au> wrote:
>
> Another approach might be to simply narrow down what valid "attribute"
> methods look like. Does it have to have a foo=3D() and foo() pair? Does
> foo() have to be parameterless, or is it accept optional parameters
> (like Ara's traits)? Then you can just pull those methods out of the
> class:
>
> class Module
>   def attributes
>     instance_methods.select do |name|
>       next if name =3D~ /!$/ || name =3D~ /=3D$/
>       setter =3D name.sub(/\?$/, "") + "=3D"
>       instance_methods.include?(setter) &&
>         [0, -1].include?(instance_method(name).arity) &&
>         [1, -2].include?(instance_method(setter).arity)
>     end
>   end
> end
>
> struct =3D Struct.new(:foo, :bar)
> [Dir, File, IO, Hash, Thread, Struct::Tms, struct].each do |c|
>   p [c, c.attributes]
> end
>
> =3D> [Dir, ["pos"]]
> [File, ["sync", "lineno", "pos"]]
> [IO, ["sync", "lineno", "pos"]]
> [Hash, ["default"]]
> [Thread, ["abort_on_exception", "priority"]]
> [Struct::Tms, ["cutime", "cstime", "stime", "utime"]]
> [#<Class:0x2c32660>, ["bar", "foo"]]
>
> Cheers,
> Dave
>
>

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