Well, Mirko, I don't know Eiffel (though I have read
about it).

My impression is that these two languages don't have
much in common. However, the principle we were 
discussing is one that Bertrand Meyer stressed in his
book _Object-Oriented Software Construction_ -- an
excellent book, though a few years out of date now.

Dave aptly called this the "uniform access principle."
I haven't heard that term used before, but I'll buy it.

But as far as Eiffel is concerned, I don't think I'd
spend all that much time on it. 

The technique of programming "by contract" is a very
appropriate method overall, but it is not unique to
Eiffel. Oh, Eiffel's design certainly facilitates it, 
but it can be done in other languages.

My advice, for what it's worth: Treat Eiffel as a 
learning exercise. It has some nice features -- the
application of the u.a. principle, the features that
help in contractual design, and a reasonable way of
handling multiple inheritance.

But in terms of learning a language that will be in
widespread use and widely available on many platforms...
spend the time practicing your Ruby instead. :) :)

Just my opinion.

Cheers,
Hal