From: Gavin Sinclair <gsinclair@...>
Date: 2002-11-14T09:43:59+09:00
Subject: Re: Keyword arguments?

From: "ahoward" <ahoward@fsl.noaa.gov>


> On Tue, 12 Nov 2002, Vis Mike wrote:
>
> [snip]
> > Keyword arguments help with ambiguity.
> [snip]
>
> this is close
>
> class Person
>   def initialize args
>     @name = args[:name]
>     @age  = args[:age]
>   end
> end
>
> me = Person.new :name => 'ara', :age => 30
>

Amidst all the discussion of various ways of achieving keyword arguments or
similar, one really nice feature has been overlooked: easy default arguments.
Here is a representation of code I've written recently.

class Recorder
  def initialize(init_params={})
    init = process_params(init_params)
    @database = init[:DATABASE]
    @user     = init[:USER]
    @password = init[:PASSWORD]
  end

  def Recorder.init_defaults
    {
       :DATABASE = "...",
       :USER     = "...",
       :PASSWORD = "...",
    }
  end

  def process_params(hash)
    defaults = init_defaults()
    # Guard user against invalid keys
    hash.keys.each do |key|
      raise "Key not supported: #{key}" unless defaults.has? key
    end
    defaults.update(hash)
  end
end


Now,
  Recorder.new  and
  Recorder.new(:USER => "smith", :PASSWORD => "apple")
will use the appropriate defaults, and
  Recorder.new(:LOG_FILE => "x.log")
will fail with a meaningful error message.

Further, if anyone wants to find out the defaults, they only have to ask:
  Recorder.init_defaults

I've been very happy with this, and see no need for Ruby to adopt explicit
keyword arguments.

Gavin