From: Wyss Clemens <WYS@...>
Date: 2002-02-13T23:05:51+09:00
Subject: RE: reducing redundancies

Below is a very rudimentary approach. Hope this suffices to get the idea.

class Module
  def persistentMembers(*members)
    memebers.each { |member|
      createGetter(member)
      createSetter(member)
    }
    createInitialize(*members)
  end
  def createGetter(memberName)
    eval("def #{memberName};<the code for the getter goes here>;end")
  end
  ...
end

class SomeStuff
  persistentMembers(:foo, :bar, :baz)
end

Instead of making "persistentMemeber" a Module(/Class) method you could
create a mixin module for persistency. Might be even cleaner!

Clemens

> -----Original Message-----
> From: Martin Maciaszek [mailto:mmaciaszek@gmx.net]
> Sent: Mittwoch, 13. Februar 2002 14:14
> To: ruby-talk@ruby-lang.org
> Subject: reducing redundancies
> 
> 
> For my project I created some objects that store all data in a
> database. All accessors get/set theirs values from/to the
> database. I finally ended up with something like this:
> 
> class Somestuff
>   @@ATTRIBUTES=%w{ foo bar baz }
>   def initialize(foo, bar, baz)
>     # do some database magic
>     @@dbh.do("insert into sometable ("+ @@ATTRIBUTES.join(", ")+
>     " ) values (" + @@ATTRIBUTES.collect { |x| "'" + eval( x ) +
>     "'"}.join(", ") +");"
>     @id=some id referencing the row created
>   end
>   def foo
>     self.genericReadAccessor "foo"
>   end
>   # similar accessors for bar and baz
>   def foo=(anotherFoo)
>     self.genericWriteAccessor "foo", anotherFoo
>   end
>   # once again similar accessors for bar and baz
>   def genericReadAccessor(anAttribute)
>     @@dbh.select_one("select #{anAttribute} from sometable"+
>     "where id=#{@id};" )[0]
>   end
>   def genericWriteAccessor(anAttribute, aValue)
>     @@dbh.do("update sometable set set"+
>     "#{anAttribute}='#{aValue}' where id=#{@id};" )
>   end
> end
> 
> What's the point of the lengthy example you ask? Count how often
> I had to write "foo" (or "bar" or "baz"). This is unneccesary
> redundancy. What happens when sometime in the future "foo" gets
> renamed to "qux"? Who's the poor bastard who has to change all
> occurences? (probably me with some help of sed, but that's not
> the point)
> 
> Is there some way to reduce those redundancies? Ideally I would
> just add an new element to the @@ATTRIBUTES and everything would
> be fine.
> 
> Any suggestions?
> 
> Cheers
> Martin
>