From: "Ara.T.Howard" <ahoward@...>
Date: 2004-01-14T16:11:39+09:00
Subject: Re: What object-configuration approach to use?

On Wed, 14 Jan 2004, Mike Williams wrote:

> Date: Wed, 14 Jan 2004 13:04:24 +0900
> From: Mike Williams <mwilliams@agentissoftware.com>
> Newsgroups: comp.lang.ruby
> Subject: What object-configuration approach to use?
> 
> Consider a class that supports a number of configurable properties.  
<snip>


> ----
> 3. OptionalArgumentMap
> 
> Another alternative is pass in a map of named optional args, e.g.
> 
>     class Link 
>         def initialize(url, content, args = {})
>           @url = url
>           @content = content
>           @title = args[:title]
>           @target = args[:target]
>         end
>     end 
> 
>     link = Link.new("http://", "here", {:title => "the whole story"})
>     helplink = Link.new("/help", "help" {:target => "helpFrame"})
> 
> As I understand it, there's some syntax-sugar planned for Ruby-2.0, that
> would make this a bit cleaner:
> 
>     link = Link.new("http://", "here", title: "the whole story")
> 
> Right?

i use variations of this alot:

  ~/eg/ruby > cat foo.rb
  module M 
    def hashify(*args); args.inject({}){|h,a| h.update a}; end
  end

  class C
    include M 
    attr :opts
    attr :foo, true
    attr :bar, true
    def initialize(*args)
      @opts = hashify(*args)
      @opts.map{|k,v| send "#{ k }=".intern, v}
    end
  end


  c = C.new :foo => 42,
            :bar => 42.0

  d = C.new c.opts, 'bar' => 'over-ridden'

  p c.foo
  p c.bar
  p d.foo
  p d.bar

  ~/eg/ruby > ruby foo.rb
  42
  42.0
  42
  "over-ridden"


it's great way to get up and running quickly and not need to change function
prototypes (read 'interface') so often.  as the need arises for type/range
checking, etc. i just do

  def foo= value
    raise unless Array = value
    @foo = value
  end

etc.

i've found this to be very useful for at least a couple of reaons:

  * keeps prototypes short
  * keeps interface consistent - it never changes ;-) 
  * allows 'argumement inheritence' (see above)
  * makes it _easy_ to pass in options from command line to objects or yaml
    configs 
  * reads nice IMHO - i never forget what each parm is since it's named

      Connection.new :port => 80, :type => 'udp'

        vs

      Connection.new 80, 'udp'

  * allows one to quite easily pass a new parameter to a deeply nested method
    without changes 40 prototypes on the way down

about the only thing i can say is that i makes it quite important to doccument
your methods so it is known what parameters a method expects.  on the other
hand it easy enough to make methods throw a 'usage' exception with details of
calling semantics.


-a
-- 

ATTN: please update your address books with address below!

===============================================================================
| EMAIL   :: Ara [dot] T [dot] Howard [at] noaa [dot] gov
| PHONE   :: 303.497.6469
| ADDRESS :: E/GC2 325 Broadway, Boulder, CO 80305-3328
| STP     :: http://www.ngdc.noaa.gov/stp/
| NGDC    :: http://www.ngdc.noaa.gov/
| NESDIS  :: http://www.nesdis.noaa.gov/
| NOAA    :: http://www.noaa.gov/
| US DOC  :: http://www.commerce.gov/
|
| The difference between art and science is that science is what we
| understand well enough to explain to a computer.  
| Art is everything else.  
|   -- Donald Knuth, "Discover"
|
| /bin/sh -c 'for l in ruby perl;do $l -e "print \"\x3a\x2d\x29\x0a\"";done' 
===============================================================================