[ruby-talk:23789] Re: RCR: Fun with attribute shortcuts solves RCR #3 and more

Wow, keep this up and you can boil a whole application down into a single 
obtuse statement :-)

On Monday 29 October 2001 04:45 pm, you wrote:
> Hi everyone, remember this?
>
> >I'm constantly creating small classes, and many of them start something
> >like:
> >  class Msg
> >    def initialize(name, type, txt)
> >      @name, @type, @txt = name, type, txt
> >    end
> >    # ...
> >  end
>
> Yeah, it's a classic, RCR #3.  We all hate repetition and typing
> stuff that is obvious, right?
>
> Last time it was Joe McDonald who said:
> > and if you have a sec, vote on RCR #3.  It's a pet peeve of mine.
>
> I think it's a pet peeve for a lot of us but I can see why
> RCR #3 was rejected as it stands now.
> What would it mean for example, if you created another
> function in the same way, like def func(@instance_var) -
> is @instance_var assigned also in that case?
> If not, why should there be a special case for initialize?
>
> So instead I propose to extend on the much loved shortcut
> methods that exist for accessors.
>
> I.e. attr_accessor :a, :b, :c creates getters and setters for
> @a, @b and @c so why not:
>
> class Mine
>     attr_initializer :a, :b, :c
>     ...
> end
>
> attr_initializer creates an initializer
> for them:
>
> def initialize(a, b, c)
>   @a, @b, @c = a, b, c
> end
>
> So there's the idea - I thought it was quite nice but
> now comes the fun part.  I love this - when you get a good idea,
> often it's easy to implement in Ruby without touching any
> interpreter or such!   For example, if you didn't get this yet,
> notice that "attr_accessor" and the like are described in docs as
> being just plain methods, in the class Module!
>
> So in some spare time at RubyConf and OOPSLA I fooled around with this
> and got really positive responses, for example at the BOF session
> at OOPSLA.
> Trying it out for real makes a much better impact.
> Using the eval-family of functions and the open classes, for
> example "Class" and "Module", you can do a lot of cool stuff
> that looks a lot like extentions of the language syntax, so here
> is my implementation of attr_initializer:
>
> # file: AttrInitializer
> class Module
>    def attr_initializer(*attrs)
>       alist = plist = ""
>       attrs.each do |v|
>          alist += "@#{v},"     # >> @var1,@var2,@var3, ...
>          plist += "#{v},"      # >> var1,var2,var3, ...
>       end
>       alist.chop!; plist.chop! # Remove last comma
>       class_eval "def initialize(#{plist}); #{alist} = #{plist}; end"
>    end
> end
>
> Since the Class class inherits from Module, now you can just
> require this file and you are able to use the attr_initializer
> shortcut in all classes.
>
>
> OK, now let's keep it going.  What else is common to define in many
> classes?  Well, the default definition of equality is that the
> compared references must be refs to the same object.  However, it is
> more common to want to compare (part of) the inner state of objects
> and if they are equal, then the two different objects should be
> considered equal.
>
> So you end up often defining == in your classes, like this, right?
>
> class Mine
>    attr_accessor :foo, :bar, :moo
>    # @foo, @bar, and @moo are my
>    # important inner state
>
>    def ==(obj)
>       @foo = obj.foo &&
>       @bar = obj.bar &&
>       @moo = obj.moo
>    end
> end
>
> Nowadays I just do this:
>
> class Mine
>    attr_equality :foo, :moo, :bar
>    ...
> end
>
> Another option is to leave out the names of objects to make
> it even simpler.  This requires the equality function to introspect
> self and the compared object to find all their instance vars.
>
> class Mine
>    attr_equality
>    ...
> end
>
> I won't post the implementation of attr_equality because it's
> longish, to support also the second option but you get the
> idea from the attr_initializer example.
>
> I'll make an RCR for this and we'll see if people like it.
> If you want a full implementation of both shortcuts
> with some tests to go with them Drop me an email directly.
> Don't reply to the list by mistake...
> (Yes, XP-enthusiasts, I wrote the tests first! Great isn't it?
> Although I updated them to run with Lapidary later)
>
> Have fun
>
> /Gunnar
>
> ---
> Gunnar Andersson
> gand -at- acm.org
>
>
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