From: Victor Shepelev <vshepelev@...>
Date: 2006-04-14T05:52:01+09:00
Subject: Re: Rubyesque way to do multiple <=>

> > I have class with some fields
> >
> > class Human
> >   attr_accessor :sex, :age, :second_name, :first_name
> > end
> >
> > now I want to sort objects of this class. I've defined operator <=>
> >
> > class Human
> >   def <=>(other)
> >     [sex, age, second_name, first_name] <=> [sex, age, second_name,
> > first_name]
> >   end
> > end
> >
> > Looks good, yeah? But! If I use third-party complex comparator for some
> of
> > the fields, I receive something like:
> >
> > def <=> (other)
> >   res = ComplexCustomComparator.compare(sex, other.sex)
> >   return res if res != 0
> >
> >   #if they have the same sex, do other comparisons
> > end
> >
> > Foooooo!
> >
> > How can I do the former in more elegant way?
> >
> > Thanks.
> >
> > Victor.


> Actually you just use your first version of method <=> without worrying
> about the second.
> Run the following code and you will clearly see why ;)
> ------------------8<-------------------------------
> class A
>     def <=>(other)
>         puts "<=> in A"
>         0
>     end
> end
> 
> puts "If at first you do not succeed"
> [1, A.new] <=> [2, A.new]
> puts "..."
> [A.new ] <=> [A.new]
> ----------------------->8----------------------------
> 
> Ruby takes care of everything for you

You haven't got it. I already USED first version, but I CAN'T if comparison
is done through stand-alone function instead of <=>

> Cheers
> Robert

Victor.