Is D slow?

[Steven Schveighoffer via Digitalmars-d-learn]

On 6/9/17 3:29 PM, Honey wrote:
> On Friday, 9 June 2017 at 18:32:06 UTC, Steven Schveighoffer wrote:
>> Wow, so that's how D code would look like if it were C++ :)
>
> Well, I cannot (and did not try to) hide where I am coming from. ;-)

hehe this was meant more as a dig at C++ syntax and not you, I totally 
understand the reason you did it that way.

Just to show you what I meant, I changed your code to eliminate the 
functors completely, the main function now looks like this:


     foreach (i;  0 .. N)
     {
         insertionSort!((a, b) => lt(a, b))(v);
         insertionSort!((a, b) => lt(b, a))(v);
     }

I'm sure there's also a way to reduce the initialization of the array to 
a few lines (or maybe even one?), but didn't have time to think about it.

>> I did replicate that issue on my box, and mucking around with the
>> implementation didn't help.
>>
>> In answer to the subject, no D is not slow. However, it's quite
>> possible that std.algorithm.bringToFront is slower than std::rotate,
>> or SortedRange.upperBound is slower than std::upper_bound, or both. I
>> don't think it's a design issue per se, probably more of an
>> implementation issue.
>
> Thank you for confirming the results and your factual explanation
> notwithstanding my pointed question. ;-)
>
> Maybe I was expecting too much given Andrei's performance oriented
> talks. I realize that the conceptual groundwork is more important than a
> concrete implementation that can be easily improved. However, I think
> that real world out-of-the-box performance - particularly with respect
> to toy examples (since those are small enough to be literally
> translated) - is important for prospects to gain confidence in buying
> into D.

Well, D is pretty fast, as fast as C++ or C. What I mean is that there 
is no inherent overhead -- both can produce exactly the same code.

However, there are some parts of C/C++ that have been optimized to 
death. It's one of those things where D's version of rotate probably 
hasn't had as much scrutiny as C++'s version. We are always looking to 
improve such things, and more investigation and suggestions are most 
welcome! It's why I filed the bug report.

> At the current state, at least for such benchmarks, I think, I should
> not rely on standard library facilities. Unfortunately, that does not
> increase my confidence.

Try to find something besides insertion sort to test with I think ;) D 
is pretty fast at a lot of things, and pleasant to write. You just found 
one test case that isn't (and we will fix it, I'm sure).

-Steve