Re: [boost] Interest for a perl6-like-junctions-class?

From: David Abrahams (dave_at_[hidden])
Date: 2005-08-04 10:30:01

Liu Jin <cpp_at_[hidden]> writes:

>>>>>> "David" == David Abrahams <dave_at_[hidden]> writes:
>     > Anyway, saying that symmetry requires
>     >      none_of(a) == any_of(b)
>     >   to be equivalent to
>     >      any_of(a) == none_of(b)
>     > is about as valid as saying
>     >      3*x == 1+y
>     >   must be equivalent to
>     >      1+x == 3*y
>     > It makes no sense to me.
>
> But it does break symmetry when
>       none_of(a) == any_of(b) [no x in a equals to any y in b]
> is different from
>       any_of(b) == none_of(a) [some x in b equals to nothing in a]

Yes.  But as I said earlier, I don't think it's important for == to be
symmetric in this case.  You had no problem reading the different
meanings of those two expressions.  Unless people start putting
any_of(b) in containers (which we can easily prevent) I think the risk
of having an assymetric equality operator is vanishingly low.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com