From: Robert Klemme <shortcutter@...>
Date: 2010-05-16T18:25:12+09:00
Subject: Re: class best way for getters ?

On 16.05.2010 09:25, Une Bévue wrote:
> Une Bévue<unbewusst.sein@google.com.invalid>  wrote:
>
>> Then, I'll have a look on Struct.
>
> i had a first look and i wonder how to use it in order to get a new
> class "HFSFile" which can be used such a way, using OpenStruct :
>
> hfsf = HFSFile.new(a_path)
> p hfsf.path
> p hfsf.modification_date
> ...
>
> because i do :
>
> class HFSFile
>    def initialize(a_path)
>      @attr = {}
>      @attr[:path] = a_path
>      @attr[:modification_date] = ...
>      ...
>      @data = OpenStruct.new(@attr)
>    end
>    def attributes
>      return @attr
>    end
>    def data
>      return @data
>    end
> end
>
> what is ennoying me in that case is in that i do have to use :
> hfsf = HFSFile.new(a_path)
> p hfsf.data.path
> p hfsf.data.modification_date
> ------^^^^^^-----------------
> ...
> where i would prefer having self being an OpenStruct (extension ?) but i
> think i can't do :
> self = OpenStruct.new(@attr)
>
> ???

There is no need for delegation here: you only need one instance and the 
way through Hash or OpenStruct seems a detour here - at least if the set 
of fields is fixed.  Then you can do

HFSFile = Struct.new :name, :modification_date do
   def self.parse(s)
     o = new
     s.scan /\s*([\w\s]+):\s*([^,]+),?/ do
       field = normalize($1)
       val = $2.strip
       o[field] = val
     end
     o
   end

   def self.normalize(k)
     k.strip.gsub /\s+/, '_'
   end
end

Now you can do:

irb(main):033:0> HFSFile.parse "name: the_name_value, modification date: 
the date"
=> #<struct HFSFile name="the_name_value", modification_date="the date">
irb(main):034:0>

You'll get a NameError if you parse fields from the String that are not 
present in the struct.  If you need to cope with additional fields you 
need to either ignore them or store them in an additional Hash member. 
You can use HFSFile.members (or just members in method parse()) to test 
for field presence.

Kind regards

	robert

-- 
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