Re: class best way for getters ?

On 05/15/2010 04:42 PM, Une B=E9vue wrote:
> i have a class "HFSFile" initialized by a parsed string
> after initialization i get a Hash @attr with keys like :name,
> :creation_date etc...
>=20
> what is the best way to write a getter for each individual key ?
>=20
> the obvious would be for example :
>=20
> def name
>   @attr[:name]
> end
>=20
> or does exist a more clever way to get all of those getters ?
> (same name for the getter that the key symbol)

You can use this:

irb(main):017:0> o =3D Object.new
=3D> #<Object:0xa1feb18>
irb(main):018:0> ha.each {|k,| class<<o;self;end.class_eval {attr k}}
=3D> {:foo=3D>2, :bar=3D>3}
irb(main):019:0> o.foo
=3D> nil
irb(main):020:0> o.bar
=3D> nil
irb(main):021:0>

Or define method_missing to fetch data from the Hash.

def method_missing(s,*a,&b)
   if a.empty? && @attr.has_key? s
     @attr[s]
   else
     super
   end
end

I would not do it though as it is not too fast.

> another way :
>=20
> def [a_key]
>  return nil unless @attr.keys.include?(a_key)
>  return @attr[a_key]
> end
>=20
> something like that ?

You could use OpenStruct

irb(main):001:0> require 'ostruct'
=3D> true
irb(main):002:0> ha =3D {:foo =3D> 2, :bar =3D> 3}
=3D> {:foo=3D>2, :bar=3D>3}
irb(main):003:0> os =3D OpenStruct.new(ha)
=3D> #<OpenStruct foo=3D2, bar=3D3>
irb(main):004:0> os.foo
=3D> 2
irb(main):005:0> os.bar
=3D> 3
irb(main):006:0>

But the question remains, whether this is a good idea.  Think about it:=20
either you do not know keys beforehand.  Then you can only use generic=20
algorithms (i.e. query all keys and print their values).  Or you do know =

keys beforehand and then you want to explicitly access individual keys=20
(e.g. obj.name).

If you know the names you can use Struct, e.g.

irb(main):011:0> St =3D Struct.new :foo, :bar
=3D> St
irb(main):012:0> s =3D St[*S.members.map{|m| ha[m]}]
=3D> #<struct St foo=3D2, bar=3D3>
irb(main):013:0> s.foo
=3D> 2
irb(main):014:0> s.bar
=3D> 3
irb(main):015:0>

Kind regards

	robert

--=20
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/