From: Logan Capaldo <logancapaldo@...>
Date: 2006-02-17T07:48:12+09:00
Subject: Re: OT: Is this worth a try?


On Feb 16, 2006, at 3:36 PM, Jim Weirich wrote:

> Logan Capaldo wrote:
>> class C < A
>>    def meth(n)
>>     precondition: n > 2 #Will not compile, C#meth accepts a narrower
>> range of inputs than A, does not follow Liskov Substitution Principle
>>    end
>> end
>
> Actually, in Eiffel, this wouldn't be a compile error.   
> Preconditions in
> a derived class is logically ORed with the those in the parent class.
> So that the full precondition for C#meth will be
>
>     precondition: (n > 2) || (n > 1)
>
> Since the preconditions are ORed, they can only be widened in derivied
> classes.  If you were using full Eiffel syntax, you would state  
> derived
> class preconditions with "require else" rather than the plain  
> "require"
> to help you remember that you can only widen the preconditions.
>
> Likewise postconditions in derived classes are ANDed with those in
> parent classes, so they can only be narrowed (and "ensure and" is used
> rather than the vanilla "ensure" [1]).
>
> --
> -- Jim Weirich
>
> [1] Ensure in the Eiffel sense (defining preconditions) rather than
> ensure in the Ruby sense (finally blocks).
>
> -- 
> Posted via http://www.ruby-forum.com/.
>

See if I ever try to clarify what someone else said ever again. I get  
twenty closet Eiffel freaks attacking my pseudo-Ruby ;)



(I'm kidding...)