On Mar 13, 4:42 am, "Robert Klemme" <shortcut... / googlemail.com>
wrote:
> 2008/3/13, Trans <transf... / gmail.com>:
>
> > Which approach is better: parametric module or an injecting class
> >  method.
>
> Are you writing a book on best practices?  There seem to be quite a
> few of these questions recently. :-))

Ha... I probably should be! But right now I'm just working through
some old "TODO" questions in Facets.

> >   # Generates identity/key methods based on specified attributes.
> >   #
> >   #   equate_on :a, :b
> >   #
> >   # _is equivalent to_
> >   #
> >   #   def ==(o)
> >   #     self.a == o.a && self.b == o.b
> >   #   end
> >   #
> >   #   def eql?(o)
> >   #     self.a.eql?(o.a) && self.b.eql?(o.b)
> >   #   end
> >   #
> >   #   def hash()
> >   #     self.a.hash ^ self.b.hash
> >   #   end
>
> >   def equate_on(*fields)
> >     code = ""
> >     code << "def ==(o) "   << fields.map {|f| "self.#{f} ==
> >  o.#{f}" }.join(" && ")    << " end\n"
> >     code << "def eql?(o) " << fields.map {|f| "self.#{f}.eql?
> >  (o.#{f})" }.join(" && ") << " end\n"
> >     code << "def hash() "  << fields.map {|f|
> >  "self.#{f}.hash" }.join(" ^ ")          << " end\n"
> >     class_eval( code )
> >     fields
> >   end
>
> I opt for the second solution because the anonymous module does not
> have any reuse effects - unless you cache it based on field names. :-)

:) And if we do cache based on field names?

T.