From: Mathieu Bouchard <matju@...>
Date: 2001-03-10T01:27:34+09:00
Subject: [ruby-talk:12336] Re: Q re looping structures

On Sat, 10 Mar 2001, ts wrote:
> >>>>> "M" == Mathieu Bouchard <matju@sympatico.ca> writes:

> M> a=[7]; a<<a
> M> b=[7,[7]]; b[1]<<b
> M> a==b

> >> -:4:in `==': detected recursive container object (TypeError)
> M> No, I mean, if we were to say that such structures should be comparable,
> M> i.e. if the result of a==b should be true or false, which one would you
> M> pick and why?
>  You have the response. In this case you can't give a result, this is why
>  it give an error message.
>  Perhaps Christoph Rippel can better explain it.



Ok, I thought it would be possible to answer "true" meaningfully.

If the comparison is topological, the answer is obviously "false", but I
don't think == should compare topology: only values should be compared, so
that a=[[42]];a<<a[0] and [[42],[42]] stay equal.

OTOH, comparing only values, given any amount of time, the system cannot
answer "false". And comparing object ids (as a helper) the system can also
terminate and return true.



matju