From: transfire@...
Date: 2006-06-03T15:14:23+09:00
Subject: Re: An alternative to the class Foo < Struct.new(vars) idiom and SuperStruct


ara.t.howard@noaa.gov wrote:
> On Fri, 2 Jun 2006 transfire@gmail.com wrote:
>
> >
> > Hal Fulton wrote:
> >> That's another example of why I would like a data structure
> >> that  1) had a convenient notation for literals and 2) was
> >> "like" a Hash, but ordered.
> >
> > Facet's has Association which gives one something quite like that.
> >
> >  [ :a >> 1, :b >> 2 ]
> >
> > Of course it does take over the #>> operator, so it can't be used
> > inside any class that defines it. But that's not a big deal. It just
> > means you can't _extend_ the following classes with code that uses an
> > Association.
> >
> >  Bignum
> >  Fixnum
> >  Date
> >  IPAddr
> >  Process::Status
> >
> > T.
>
> that just gave me an idea:
>
>      harp:~ > cat a.rb
>      require 'arrayfields'
>      class Map < Array
>        class Pair < Array; end
>        def initialize *pairs
>          fields = []
>          pairs.each{|k, v| self << v and fields << k}
>          self.fields = fields
>        end
>        def self.[](*a, &b) new(*a, &b) end
>      end
>      class Symbol
>        def >(value) Map::Pair[self, value] end
>      end
>      def Map(*a, &b) Map.new(*a, &b) end
>      def map(*a, &b) Map.new(*a, &b) end
>
>
>      m = map :a > 4, :b > 2
>      p m
>      p m[:a]
>      p m[:b]
>      p m.to_hash
>      p m.keys
>
>
>      harp:~ > ruby -r rubygems a.rb
>      [4, 2]
>      4
>      2
>      {:b=>2, :a=>4}
>      [:a, :b]
>
>
> what do you think?

Cool. Pair is a lot like Association but you've added the Map class
here. Of course you've limited yourself to symbol keys by using >.
Using Associations does have some limitations as far as being a full
fledged omap, since it's just an Array of Associations, but it would be
easy enough to combine it with your map class. Put the two together and
have:

  m = map :a>>4, :b>>2

Nice thing about Associations too is that have some other uses as well.
The only thing that would be better is a literal form and perhaps a
slighlty better operator.

T.