From: "Aaron D. Gifford" <astounding@...>
Date: 2011-04-15T08:45:30+09:00
Subject: Re: What do you do when you need to attach data to an object instance?

> On Thu, Apr 14, 2011 at 3:11 PM, Kevin Mahler <kevin.mahler@yahoo.com> wrote:
>> You probably wouldn't want OpenStructModule even if it did exist because
>> you wouldn't want NoMethodError to be suppressed. Perhaps you're looking
>> for Object#extend.

So using Kevin's suggestion:

def extend_accessor(obj, name)
  mod = Module.new
  mod.send(:public).send(:attr_accessor, name.to_sym)
  obj.extend(mod)
  obj
end

That's a cleaner way to attach data:

irb(main):001:0> def extend_accessor(obj, name)
irb(main):002:1>   mod = Module.new
irb(main):003:1>   mod.send(:public).send(:attr_accessor, name.to_sym)
irb(main):004:1>   obj.extend(mod)
irb(main):005:1>   obj
irb(main):006:1> end
=> nil
irb(main):007:0> a = "this is a string"
=> "this is a string"
irb(main):008:0> extend_accessor(a, :bar)
=> "this is a string"
irb(main):009:0> a.bar
=> nil
irb(main):010:0> a.bar = "hi there"
=> "hi there"

Now another question.  I noticed that if I don't include the
send(:public) bit up there, that the send(:attr_accessor) message
delivered to the anonymous module ends up creating private accessor
methods, not public.

I find that puzzling:

irb(main):001:0> def extend_accessor(obj, name)
irb(main):002:1> mod = Module.new
irb(main):003:1>   mod.send(:attr_accessor, name.to_sym)
irb(main):004:1> obj.extend(mod)
irb(main):005:1> obj
irb(main):006:1> end
=> nil
irb(main):007:0> a = "this is a string"
=> "this is a string"
irb(main):008:0> extend_accessor(a, :bar)
=> "this is a string"
irb(main):009:0>  a.bar = "hi there"
NoMethodError: private method `bar=' called for "this is a string":String
	from (irb):9
	from /opt/local/bin/irb:12:in `<main>'
irb(main):010:0>

Any ideas why sending :attr_accessor to a module would create
accessors as private?

I would think that attr_accessor implies public, but I guess if by
default an anonymous module is in "private" mode, that might explain
it.

However, if that's the case, why does this work to create public methods:
def extend_method(obj, name, &block)
  mod = Module.new
  mod.send(:define_method, name, &block)
  obj.extend(mod)
  obj
end

Sending define_method (at least for me) to an anonymous Module seems
to default to "public" mode.  This seems a tad inconsistent.

All this was on Ruby 1.9.2 on a FreeBSD box.

Aaron out.