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

From: David Abrahams (dave_at_[hidden])
Date: 2005-08-03 05:11:47

Rob Stewart <stewart_at_[hidden]> writes:

> Florian's notion of these operators, derived from Perl, is that
> they are not symmetrical.  To make expressions like 1 and 2
> symmetrical, I've taken to swapping arguments depending upon the
> combination of types, which means I'm forcing the symmetry.
> Maybe I'm just off the mark and they should be allowed to be
> asymmetrical.

I think that's right.  These things reflect the syntax and semantics
of english, not of math anymore.

Besides, >, >=,<=, < aren't symmetric ;^)

>> > Reasoning
>> > over the result of using none_of() with a user-defined predicate
>> > gets quite difficult when compared against an all_of() or other
>> > junction/multivalue objects.  Doing so against a single value is
>> > much easier.
>> >
>> Yes but the documentation should say what combinations
>> are potentially dangerous.
>
> Dangerous?  Inefficient or useless, maybe, but dangerous?
>
>> > I think "evaluate" is better than "is_true_that:"
>> >
>> >   if (evaluate(all_of(a), _1 >= _2, one_of(b))) ...

Yuck.

>
> Perhaps we should consider a functional style:
>
>    if (compare(all_of(a), one_of(b), _1 >= _2))
>
> or
>
>    if (compare(all_of(a), _1 >= _2, one_of(b)))

IMO that's a *lot* harder to read than

    all_of(a) >= one_of(b)

I'm not sure if I'm going to like the latter style in the long run,
but so far it's looking pretty sweet.

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