Re: Setter method for Hash value

On Fri, Feb 4, 2011 at 5:03 PM, Rolf Pedersen <[e-mail]> wrote:
> Hi Jesus
>
> It does seem to be working. At least the example "requirements" that I
> defined does give the expected response.
> I have to admit, I need to study this a bit, to figure out HOW it is
> working, though. ;o)

You have two sets of requirements:

1.- Calls on the instance of MyClass: props and props=
2.- Calls on the object returned by the previous props calls: [] and []=

You need to forward these 4 calls to another class. The first two are
easy: we just implement the MyClass#props and MyClass#props= to do
what we want.

For the other two, you need a proxy object that can delegate [] and
[]= to DataClass too. For this to work, MyClass#props needs to wrap
the actual hash returned by DataClass with a wrapper object (Props).
As you need this proxy object to have some hash like behaviour, you
can implement whatever methods you need to behave like a hash. As an
example, apart from [] and []= I have implemented inspect and to_s.


On Fri, Feb 4, 2011 at 3:45 PM, Brian Candler <[e-mail]> wrote:

> Try to avoid class variables. An instance variable of the class (@data)
> would work just as well here. @@var has really strange semantics which I
> can never entirely remember, and once you've been bitten by them, you'll
> choose to use instance variables as well.

I completely agree. I was in a rush when I wrote my previous post, so
I left it as it is. Using instance variables on the DataClass object
is cleaner:

irb(main):030:0> class DataClass
irb(main):031:1>  @data = {:a=>1, :b=>2, :c=>3}
irb(main):032:1>  def self.get_props()
irb(main):033:2>    @data
irb(main):034:2>  end
irb(main):035:1>  def self.get_prop(key)
irb(main):036:2>    @data[key]
irb(main):037:2>  end
irb(main):038:1>  def self.set_props(data)
irb(main):039:2>    @data = data
irb(main):040:2>  end
irb(main):041:1>  def self.set_prop(key, value)
irb(main):042:2>    @data[key] = value
irb(main):043:2>  end
irb(main):044:1> end
=> nil
irb(main):045:0> c = MyClass.new
=> #<MyClass:0xb7881b40>
irb(main):046:0> c.props
=> {:b=>2, :a=>1, :c=>3}
irb(main):047:0> c.props = {:a => 3, :b => 0, :c => 5, :d => 6}
=> {:b=>0, :a=>3, :c=>5, :d=>6}
irb(main):048:0> c.props
=> {:b=>0, :a=>3, :c=>5, :d=>6}
irb(main):049:0> c.props[:a]
=> 3
irb(main):050:0> c.props[:a] = 55
=> 55
irb(main):051:0> c.props[:a]
=> 55
irb(main):052:0> c.props
=> {:b=>0, :a=>55, :c=>5, :d=>6}

I hope it's clearer now. Let me know if you need further help
understanding this.

Jesus.