From: Trans <transfire@...>
Date: 2008-11-26T22:13:56+09:00
Subject: Re: attr_reader, default attribute value, and rdoc of attrib



On Nov 26, 7:17 am, Brian Candler <b.cand...@pobox.com> wrote:
> dkmd_nielsen wrote:
> > What I want to do is create an attribute, allow it to have a default
> > value, and have the attribute documented as such (and not as a method)
> > with rdoc.  So, would the proper syntax for accomplishing this
> > elementary feat be:
>
> >    # Field (row) delimiter.  Default is a comma.
> >    attr_reader fld_delimiter
>
> >    # :call-seq:
> >     #   fld_delimiter
> >     #
> >     # Returns the field (column) delimiter.  Default is comma.
> >     def fld_delimiter #:nodoc:
> >       !@fld_delimiter.nil? ? @fld_delimiter : (@fld_delimiter = ',')
> >     end
>
> >     # :call-seq:
> >     #   fld_delimiter(String)
> >     #
> >     # Assign a field (column) delimiter.
> >     def fld_delimiter=(d)
> >       @fld_delimiter = d
> >     end
>
> I would tidy this up as:
>
> attr_accessor :fld_delimiter
> def fld_delimiter #:nodoc:
>   @fld_delimiter ||= ','
> end
>
> That assumes you never want to assign nil or false as a fld_delimiter.
> If you do, then
>
> attr_accessor :fld_delimiter
> def fld_delimiter #:nodoc
>   @fld_delimiter = ',' unless defined? @fld_delimiter
>   @fld_delimiter
> end
>
> Another option is never to assign when defaults are being used: using a
> constant lets you document the default.
>
> DEFAULT_FLD_DELIMITER = ','.freeze
> attr_accessor :fld_delimiter
> def fld_delimiter
>   defined? @fld_delimiter ? @fld_delimiter : DEFAULT_FLD_DELIMITER
> end
>
> However I think it would be simpler just to set @fld_delimiter=',' in
> your object's initialize method.

Brain is right on. The archetypal Ruby best-practice will look like
this:

  DEFAULT_FLD_DELIMITER = ','.freeze

  attr_accessor :fld_delimiter

  def initialize
    @fld_delimiter = DEFAULT_FLD_DELIMITER
  end