On 09/16/2011 09:12 PM, Andrei Alexandrescu wrote:
On 9/16/11 1:24 PM, Simen Kjaeraas wrote:
On Thu, 15 Sep 2011 19:14:24 +0200, Jonathan M Davis
I think that that's up for debate. I would fully expect a min/max
function to
be using a comparator function, which means using a binary predicate.
This seems weird to me. min already has a binary predicate - a < b.
This predicate is what defines min, any other predicate would make it
a different function - usually reduce, unless we're talking about
argMin (does argReduce make any kind of sense?).
That said, there are cases where a < b is not enough, owing to some
types not having a nice and simple comparison. Hence, binary
predicates should also be allowed. I just feel that in the general
case, binary predicates dilute the meaning of min/max. Would you
consider this code good?
min!"a > b"(range);
That's not min, that's max. More:
min!"a.member1 < b.member2"(range);
Again, it's not min, it's something else.
This is a good argument. The "something else" is "extremum"
The "something else" is a "least element of a total order", or "min",
but using a non-standard total order to extend the set of values to an
ordered set. I don't think the argument is good.
http://en.wikipedia.org/wiki/Total_order
> (http://en.wikipedia.org/wiki/Maxima_and_minima).
That is analysis. But the topic is discrete mathematics.
I suggest:
* Introduce the algorithm "extremum" with a required predicate.
What would that do? The range has more than one extremum if it is
non-constant.
* Introduce extremumCount and extremumPos, both with required predicate.
And those will be minCount+maxCount and merge(minPos,maxPos) ?
* Keep minCount and minPos without a predicate. They'd in all likelihood
use extremum.
How?
* Deprecate minCount and minPos with predicate (this is ouchworthy but I
think it won't break a whole lot of code).
* Introduce maxCount and maxPos without predicate.
My suggestion:
* Keep minCount and minPos with predicate.
* Introduce maxCount and maxPos with predicate.
* Introduce min(range) and max(range) without predicate.
A binary predicate would be fine. The terms min or max don't have any
meanings without an ordering relation. Not giving the relation as an
argument just makes the relation implicit.
* Introduce argmin and argmax with unary predicate.
I think you meant an unary function.
Timon
