From: David Abrahams <dave@boost-consulting.com>
Rob Stewart <stewart@sig.com> 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.
That's always a bad sign! ;-)
Besides, >, >=,<=, < aren't symmetric ;^)
I swapped predicates accordingly.
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.
Do you prefer "is_true_that" or were you registering distaste for both?
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)
Of course.
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.
What about user-supplied predicates? You can't use infix notation then. -- Rob Stewart stewart@sig.com Software Engineer http://www.sig.com Susquehanna International Group, LLP using std::disclaimer;