From: Logan Capaldo <logancapaldo@...>
Date: 2006-05-07T05:23:11+09:00
Subject: Re: self.new and initialize ( was Re: Creating sub-classes using Struct)


On May 6, 2006, at 4:10 PM, Bira wrote:

> On 5/6/06, Logan Capaldo <logancapaldo@gmail.com> wrote:
>
>> I would suggest
>>
>> class Database
>>    def self.new(file_containing_info)
>>        fields = parse_field_format(file_containing_info)
>>        Database.const_set('Record", Struct.new(*fields))
>>        super
>>    end
>>
>>    def initialize(file)
>>       @records = []
>>       read_each_record_in_file(file) do |record_data|
>>            record = Database::Record.new
>>            extract_record_data_into(record_data, record)
>>            @records << record
>>       end
>>   end
>> end
>
> I think I still have a long way to go before I can write a decent,
> Ruby-ish example :). This one is a little beyond my ability to
> understand at a glance...
>
> What happens when I call Database.new(some_file) ? In which order to
> the "new" and "initialize" methods get called?
>
Basically new calls initialize, and then returns the instance of the  
object. The normal implementation of new would look something like:

class Class
   def new(*args, &block)
     obj = self.allocate
     obj.initialize(*args, &block)
     obj
   end
end

My new does some extra work by defining the Record class based on  
some info in the file. There's a big problem with my code though and  
it's called Only one database per program!. Or at least only one at a  
time

e.g.

db1 = Database.new(file1)
db2 = Database.new(file2)

if file2 has a different record format than file1, it's going to  
seriously mess up any interactions with db1. An alternative method  
would be of course to do something like

class Database
   def initialize(file)
       @Record =  Struct.new(...)
       ...
   end
end

> --
> Bira
> http://compexplicita.blogspot.com
> http://sinfoniaferida.blogspot.com
>