On Tuesday, 13 June 2017 at 14:51:40 UTC, Steven Schveighoffer
wrote:
Yes, I saw that when I was looking (you can see from my reply
that you quoted below).
Yes, I had missed that point.
Yes I think it makes sense to have such a comparison function
for non-ranges. Yes it probably belongs there, as there are
other functions (e.g. swap) that are not specific to ranges in
std.algorithm. It should probably not be called cmp, as it will
be a default comparison (with the default ordering), although
if we did something like:
int cmp(alias pred = "a < b", T)(T t1, T t2) if(!isInputRange!T)
{
static if(pred == "a < b") { /* do default optimized way */ }
else { /* more generic mechanism using pred */ }
}
it might be nice. Need to think about the API ramifications.
I retracted my earlier proposal after I had realized my
confusion. I had thought that cmp would implement three way range
comparison based on three way element comparison. Then I realized
that it is based on "a < b" or alike. The latter is certainly
useful but I am afraid that this approach does not always lead to
optimal performance.
I gathered a few ideas about the subject. I have to sit down and
write it down.
I agree. It's a thing also that can be optimized in unintuitive
ways. I think Andrei has a nice way to do opCmp for integers
that's a simple subtraction and negation or something like that.
I observed that compiler optimizers are pretty smart about
comparison of individual integers. I guess that we do not need to
be clever, here.
