From: Markus <markus@...>
Date: 2004-09-19T14:03:41+09:00
Subject: Re: bug bytes

On Sat, 2004-09-18 at 21:05, Bill Guindon wrote:

> I'm still hating the 'pack'
> statement, so I refuse to apologise to it ;)

     I suppose writing a wrapper of some sort doesn't work for you?  For
example, when I had to read & write some Pascal records (native format
binary goo) I wrote a little thing that I stuck in "module Module"
(IIRC) to define the fields, and get_record and put_record methods that
schleped the data to/from the format, and forgot about the internals as
quickly as I could.

     A quick check just now failed to turn up the code, but I can sketch
it.  

*********************************************************************
** WARNING: THE FOLLOWING CODE HAS BEEN TYPED FROM MEMORY BY SOMEONE 
** WHO SHOULD HAVE GONE TO BED SEVERAL HOURS AGO.
*********************************************************************

      * Add something that looks something like
        
        $packing_formats = {
            :integer => 'i',
            :real    => 'f',
            --etc, to suit 
            }
        class Module
            #
            # To automate the reading and writing of objects
            #
            def columns
                @columns ||= []
                end
            def pack_format
                @pack_format ||= ''
                end
            private
                def field(id,type)
                    @columns ||= []
                    id = id.to_s
                    attr_accessor id unless 
                       instances_respond_to?  id+'='
                    @columns << id
                    @pack_format = pack_format + $packing_formats[type]
                    end
            end
        
        
      * then define a pack/unpack methods something like
        
        class Object
            def pack
                self.class.fields.collect { |field|
                    self.send(field)
                    }.pack(self.class.pack_format)
                end
            def unpack(s)
                v = s.unpack(self.class.pack_format)
                self.class.fields.each { |field|
                    self.send(field+'=',v.shift)
                    } 
                end
            end
        
        
      * look into the pen with the bright red light and forget about how
        it works.  Use "field" instead of "attr_accessor" when defining
        objects that need to match external record formats

IIRC, the version I wrote for myself wound up having another level of
abstraction that made it look like an SQL-based object persistence
interface that was in use in the same program.  Then as the data storage
back-end got cleaned up it shriveled up and eventually blew away.

 -- MarkusQ