Re: Silicon Valley D Meetup - March 18, 2021 - "Templates in the D Programming Language" by Ali Çehreli
On Friday, 19 March 2021 at 17:10:27 UTC, Ali Çehreli wrote: Jon mentioned how PR 7678 reduced the performance of std.regex.matchOnce. After analyzing the code we realized that the performance loss must be due to two delegate context allocations: https://github.com/dlang/phobos/pull/7678/files#diff-269abc020de3a951eaaa5b8eca5a0700ba8b298767c7a64f459e74e1531a80aeR825 One delegate is 'matchOnceImp' and the other one is the anonymous delegate created on the return expression. We understood that 'matchOnceImp' could not be a nested function because of an otherwise useful rule: the name of the nested function alone would *call* that function instead of being a symbol for it. That is not the case for a local delegate variable, so that's why 'matchOnceImp' exists as a delegate variable there. Then there is the addition of the 'pure' attribute to it. Fine... After tinkering with the code, we realized that the same effect can be achieved with a static member function of a static struct, which would not allocate any delegate context. I add @nogc to the following code to prove that point. The following code is even simpler than Jon and I came up with yesterday. [... Code snippet removed ...] There: we injected @trusted code inside a @nogc @safe function. Question to others: Did we understand the reason for the convoluted code in that PR fully? Is the above method really a better solution? I submitted PR 7902 (https://github.com/dlang/phobos/pull/7902) to address this. I wasn't able to use the version Ali showed in the post, but the PR does use what is essentially the same idea identified at the D Meetup. It is a performance regression, and is a bit more nuanced than would be ideal. Comments and review would be appreciated. --Jon
Re: Silicon Valley D Meetup - March 18, 2021 - "Templates in the D Programming Language" by Ali Çehreli
On 3/19/21 2:45 AM, data pulverizer wrote:
> I have to say that I got an enormous amount out of it!
Thank you for attending and steering the discussion to interesting
places. It turned out to be much different from a "beginner-friendly"
presentation. :)
It was interesting to understand some code by Andrei:
https://gist.github.com/andralex/0d85df38be2d9ffbe89cf1fb51c44213#file-reify-d-L164
It was interesting to realize that the selected line above can be an
example of a use case for nested templates. Instead of the following
line where the first template parameter is implicitly the "needle" and
the rest are the "haystack"
static assert(staticIndexOf!( byte, byte, short, int, long) == 0);
we can use nested templates to have more readable code:
static assert(staticIndexOf!byte.among!(byte, short, int, long) == 0);
(Assuming 'among' is a nested template inside 'staticIndexOf'.)
> I feel energised for what I learned.
It is too nerdy to say but I could not go to sleep easily due to some
adrenaline rush! Ha ha! :D
> There was one other person who made a useful comment that
> helped my understanding whose name I don't recall - thank you
> too.
That must be Jon Degenhardt. Jon mentioned how PR 7678 reduced the
performance of std.regex.matchOnce. After analyzing the code we realized
that the performance loss must be due to two delegate context allocations:
https://github.com/dlang/phobos/pull/7678/files#diff-269abc020de3a951eaaa5b8eca5a0700ba8b298767c7a64f459e74e1531a80aeR825
One delegate is 'matchOnceImp' and the other one is the anonymous
delegate created on the return expression.
We understood that 'matchOnceImp' could not be a nested function because
of an otherwise useful rule: the name of the nested function alone would
*call* that function instead of being a symbol for it. That is not the
case for a local delegate variable, so that's why 'matchOnceImp' exists
as a delegate variable there.
Then there is the addition of the 'pure' attribute to it. Fine...
After tinkering with the code, we realized that the same effect can be
achieved with a static member function of a static struct, which would
not allocate any delegate context. I add @nogc to the following code to
prove that point. The following code is even simpler than Jon and I came
up with yesterday.
void foo(ref int i) pure @nogc @safe {
// Another local variable that will be used by the static
// function of the static struct
double d = 0.0;
/* Instead of a lambda variable like this:
auto bar = () @trusted {
// ...
};
We use a static member function of a static struct:
*/
static struct S {
static auto bar(ref int j, double e) pure @trusted @nogc {
// Doing something unsafe inside this trusted function
*(cast(int*)cast(long*)&j) += 42 + e;
// Totally unrelated: It is a shame that the 'double'
// expression on the right-hand side is added to an 'int'
// on the left-hand side but we know that. :/
}
}
// Pass needed variables instead of using them from a delegate
// context
return (&S.bar)(i, d);
/* The following more convoluted method works as well but seems
* unnecessary:
alias T = typeof(&S.bar);
enum attrs = functionAttributes!T | FunctionAttribute.pure_ ;
return (() @trusted @nogc => (cast(SetFunctionAttributes!(T,
functionLinkage!T, attrs)) &S.bar))()(i, d);
*/
}
void main() {
int i = 0;
foo(i);
assert(i == 42);
}
There: we injected @trusted code inside a @nogc @safe function.
Question to others: Did we understand the reason for the convoluted code
in that PR fully? Is the above method really a better solution?
Ali
Re: Silicon Valley D Meetup - March 18, 2021 - "Templates in the D Programming Language" by Ali Çehreli
On Wednesday, 17 March 2021 at 21:54:27 UTC, Ali Çehreli wrote: I will explain templates in a beginner-friendly way. Although this is announced on Meetup[1] as well, you can connect directly at https://us04web.zoom.us/j/2248614462?pwd=VTl4OXNjVHNhUTJibms2NlVFS3lWZz09 March 18, 2021 Thursday 19:00 Pacific Time Ali [1] https://www.meetup.com/D-Lang-Silicon-Valley/events/kmqcvqyccfbxb/ I turned up to this online meetup and I have to say that I got an enormous amount out of it! Conversations like this once a month or so a few years ago would have made me a much better programmer (and maybe even a different person) now. Ali spent a lot of time dissecting code in such an informative, cogent, and enlightening way, I'm kicking myself for not getting involved in these kinds of meetings before. Even though the scheduled time for me was 2:00am in the morning, I feel energised for what I learned. It's a bit like I was groping around in the semi-darkness and someone switched on a light bulb. Many thanks to Ali for setting this one up! There was one other person who made a useful comment that helped my understanding whose name I don't recall - thank you too.
Re: Silicon Valley D Meetup - March 18, 2021 - "Templates in the D Programming Language" by Ali Çehreli
On Thursday, 18 March 2021 at 16:12:32 UTC, Ali Çehreli wrote: Understood. Mike Parker contacted me about potentially recording this as well but unfortunately, there is no structure at all and I can't come up with anything that is worth recording in a few hours now. Let's skip this occasion and I promise I will put some slides and a recording later. So, this meeting will be more like a chat anchored on templates. Ali Ok no problem. Thanks, Matheus.
Re: Silicon Valley D Meetup - March 18, 2021 - "Templates in the D Programming Language" by Ali Çehreli
On 3/18/21 6:34 AM, matheus wrote: > But another reason that I pointed youtube > re-transmission, is that at least where I live this service has no > "buffering" for live streaming, while other services use to be pretty > bad in this regard. Understood. Mike Parker contacted me about potentially recording this as well but unfortunately, there is no structure at all and I can't come up with anything that is worth recording in a few hours now. Let's skip this occasion and I promise I will put some slides and a recording later. So, this meeting will be more like a chat anchored on templates. Ali
Re: Silicon Valley D Meetup - March 18, 2021 - "Templates in the D Programming Language" by Ali Çehreli
On Thursday, 18 March 2021 at 10:29:20 UTC, Ali Çehreli wrote: On 3/17/21 8:07 PM, matheus wrote: > Is there a way to have a Youtube re-transmission live too? - > Unfortunately I can't access this site, and I am interested in this talk. > > Matheus. This will be as informal as meetups get: There aren't even slides (yet?). :) Would jitsi work for you? If so, we may decide to move over there and I would post the meeting link and the password here at 18:55 Pacific Time, as Iain does for BeerConf. Ali I would also be interested in some recorded event since I saw now it starts 3am local time for me 😭
Re: Silicon Valley D Meetup - March 18, 2021 - "Templates in the D Programming Language" by Ali Çehreli
On Thursday, 18 March 2021 at 10:29:20 UTC, Ali Çehreli wrote: This will be as informal as meetups get: There aren't even slides (yet?). :) Would jitsi work for you? If so, we may decide to move over there and I would post the meeting link and the password here at 18:55 Pacific Time, as Iain does for BeerConf. Ali Hi Ali, Well I never tried it, but if it's possible to watch on a browser I definitely can try. But another reason that I pointed youtube re-transmission, is that at least where I live this service has no "buffering" for live streaming, while other services use to be pretty bad in this regard. Thanks for the support, Matheus.
Re: Silicon Valley D Meetup - March 18, 2021 - "Templates in the D Programming Language" by Ali Çehreli
On 3/17/21 8:07 PM, matheus wrote: > Is there a way to have a Youtube re-transmission live too? - > Unfortunately I can't access this site, and I am interested in this talk. > > Matheus. This will be as informal as meetups get: There aren't even slides (yet?). :) Would jitsi work for you? If so, we may decide to move over there and I would post the meeting link and the password here at 18:55 Pacific Time, as Iain does for BeerConf. Ali
Re: Silicon Valley D Meetup - March 18, 2021 - "Templates in the D Programming Language" by Ali Çehreli
On Wednesday, 17 March 2021 at 21:54:27 UTC, Ali Çehreli wrote: I will explain templates in a beginner-friendly way. Although this is announced on Meetup[1] as well, you can connect directly at https://us04web.zoom.us/j/2248614462?pwd=VTl4OXNjVHNhUTJibms2NlVFS3lWZz09 March 18, 2021 Thursday 19:00 Pacific Time Ali [1] https://www.meetup.com/D-Lang-Silicon-Valley/events/kmqcvqyccfbxb/ Nice! I'll try to attend 🍀
Re: Silicon Valley D Meetup - March 18, 2021 - "Templates in the D Programming Language" by Ali Çehreli
On Wednesday, 17 March 2021 at 21:54:27 UTC, Ali Çehreli wrote: I will explain templates in a beginner-friendly way. Although this is announced on Meetup[1] as well, you can connect directly at https://us04web.zoom.us/j/2248614462?pwd=VTl4OXNjVHNhUTJibms2NlVFS3lWZz09 March 18, 2021 Thursday 19:00 Pacific Time Ali [1] https://www.meetup.com/D-Lang-Silicon-Valley/events/kmqcvqyccfbxb/ Is there a way to have a Youtube re-transmission live too? - Unfortunately I can't access this site, and I am interested in this talk. Matheus.
Silicon Valley D Meetup - March 18, 2021 - "Templates in the D Programming Language" by Ali Çehreli
I will explain templates in a beginner-friendly way. Although this is announced on Meetup[1] as well, you can connect directly at https://us04web.zoom.us/j/2248614462?pwd=VTl4OXNjVHNhUTJibms2NlVFS3lWZz09 March 18, 2021 Thursday 19:00 Pacific Time Ali [1] https://www.meetup.com/D-Lang-Silicon-Valley/events/kmqcvqyccfbxb/
