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Allow environment capture in lambda callbacks#19

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Aasim-A merged 3 commits intoAasim-A:masterfrom
c-jiph:master
May 29, 2022
Merged

Allow environment capture in lambda callbacks#19
Aasim-A merged 3 commits intoAasim-A:masterfrom
c-jiph:master

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@c-jiph
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@c-jiph c-jiph commented Mar 13, 2022

Thank you for making this library, it's been really helpful for a small project of mine.

This PR adds the ability to capture variables in lambdas used as timer callbacks. For example:

AsyncTimer t;

void foo(int v) {
  t.setTimeout([=]() {
    Serial.print("Got value ");
    Serial.println(v, DEC);
  }, 1000);
}

Without something like this PR, the above will fail with an error like:

Example.ino: In function 'void foo(int)':
Example:12:10: error: no matching function for call to 'AsyncTimer::setTimeout(foo(int)::<lambda()>, int)'
   }, 1000);
          ^
In file included from Example.ino:4:0:
/home/c-jiph/Arduino/libraries/AsyncTimer/src/AsyncTimer.h:77:18: note: candidate: short unsigned int AsyncTimer::setTimeout(AsyncTimer::Callback, long unsigned int)
   unsigned short setTimeout(Callback callback, unsigned long ms);
                  ^~~~~~~~~~
/home/cjiph/Arduino/libraries/AsyncTimer/src/AsyncTimer.h:77:18: note:   no known conversion for argument 1 from 'foo(int)::<lambda()>' to 'AsyncTimer::Callback {aka void (*)()}'
exit status 1
no matching function for call to 'AsyncTimer::setTimeout(foo(int)::<lambda()>, int)'

Note this actually fixes the existing example CancelTimeoutExample.ino which currently does not compile in master.

I've also included a macro option LITE_CALLBACK_SUPPORT which enables the old implementation which will save a small amount of code and data storage for highly constrained projects.

@Aasim-A
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Aasim-A commented Mar 23, 2022

Hi Jacob, thanks for the PR, my concern is that this may not work with arduino boards because they might not support std::function have you tested that?

@c-jiph
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c-jiph commented Mar 27, 2022

Ah, you are absolutely right. The project I was working on is actually for an Arm-based Arduino board, not AVR. After checking I see STL is not available in the Arduino IDE for AVR boards.

The AVR compiler is still fully gcc with C++ backed, so I was able to update my PR to make this work without STL. The change is quite a bit more involved though. Essentially I've created a very simple replacement for std::function which only supports holding lambdas/pointers to functions with no args and no return. I got the core ideas from https://www.codeproject.com/Articles/313312/Cplusplus11-Lambda-Storage-Without-libcplusplus

It's not ... beautiful, but seems to work and I've verified it on an Arduino Uno board. The most annoying part is not having things like std::move or std::swap so there are a few more copies than I'd like.

What do you think?

@tamtakoe
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tamtakoe commented Apr 24, 2022

@Aasim-A any comments?

@VladislavSmolyanoy
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VladislavSmolyanoy commented Apr 24, 2022

Works perfectly on an ESP32

@Aasim-A
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Aasim-A commented May 6, 2022

Hi, sorry I've been super busy lately, I'll look more into this and try to merge it into the library.

Thanks again for the PR

@Aasim-A
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Aasim-A commented May 29, 2022

@c-jiph Sorry this took this long, thanks a lot for putting the time to implement this 🙂

@Aasim-A Aasim-A merged commit fc9b1b4 into Aasim-A:master May 29, 2022
@rjkiv rjkiv mentioned this pull request Sep 27, 2022
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4 participants

@c-jiph @Aasim-A @tamtakoe @VladislavSmolyanoy