Accessors and anonymous classes

Hmmm… odd I wrote a version of this last night but it would appear
that I failed to post it to the forum, doh! so here it goes again. If
it did get out and this is a duplicate then please accept my apologies
for the waste of bandwidth.

I am writing a recursive descent parser to parse a configuration file
that consists of nested ‘Sections’ which all look like this:
[ ] {


.
.
}

where may be another section.

I wrote a clase Section to parse the basic structure. Section.initialise
calls method specificItems to parse non section items (see below). For
each type of section I have an anonymous class tied to a Class variable
– I have included one such class below. I had to make the classes
anonymous because I needed to include references to the classes in a
data structure (see subSections ) which tells the parser which section
types are valid in this section and what to do with them.

[ aside: someone asked why I wanted reference to scalar variable in my
previous post – this is why. I needed to have a refernce to a variable
in that structure into which I could store the parsed class]

Now to the problem: As you see I have defined a bunch of accessor
methods using attr_reader and attr_writer, but these don’t work ( I get
an undefined method error ). Adding the accessor methods explicitly
works fine. Odd!

I’m not sure if this is a bug, a feature or simply some lack in my
understanding of how things should work.

Any ideas?

Also this is my first real OO Ruby program and I would appreciate
comments – it is too large (currently 1000 lines) to post here but if
anyone would be willing to have a look at it I’d be happy to email it to
them. My email is [email protected]

I have run into various problems in this project and have managed to
solve all of them but I am far from confident that my solution was the
best way of doing it. The use of anonymous classes is one example. I
wrote a generic text parser for this project and because Ruby does not
support multiple inheiritance I ended up passing an instance of the
parser as a parameter to all the methods – I figured that since the
parser needed to maintain state that I could not make it a mixin…

Cheers, Russell

@@hostService = Class.new( Section ) {

  attr_reader = :services, :converted, :actions, :patterns, 

:realTime,
:periodic, :files
attr_writer = :converted

  def initialize( head, parser )
    @services = []
    @actions = []
    @patterns = []
    @realTime = []
    @periodic = []
    @files = []
    @converted = false
    super( head, parser )
  end

accessor methods — since the shorthand way did not work

  def actions
    @actions
  end

[ boring repeditive stuff snipped ]

  def converted=(value)
    @converted = value
  end

this handles the non section items in the section

  def specificItem( firstToken, parser )

    case firstToken
    when 'service'
      if token = parser.expect(/^(\w+)/, "service name") then
        @services.push( token )
      else
        @errors = true
        parser.restofLine   # ignore the rest of the line
      end
    else
      @errors = true
      parser.error( "#{firstToken} not valid in host section" )
      parser.restofLine   # ignore the rest of the line
    end
 end

defines which sections may be nested within this section

Key is the section type the vailue is [ ,

class to parse section and where to store the result ]

  def subSections( kind )
    {'actions'     => [nil, @@actionList, @actions ],
     'files'       => [nil, @@commaList, @files],
     'patterns'   => [nil, @@patternList, @patterns],
     'realtime'   => [nil, @@matchList, @realTime],
     'periodic'   => [nil, @@matchList, @periodic]
    }[kind]
  end
} # end of hostSection

This forum is not affiliated to the Ruby language, Ruby on Rails framework, nor any Ruby applications discussed here.

| Privacy Policy | Terms of Service | Remote Ruby Jobs