C++ Lambdas in Arduino

I had the need to pass some callback functions to some of my generic C++ Arduino classes. So I was asking myself if we can use Lambdas in Arduino.

Here is a small test sketch, to verify this.

#include "TestLambda.h"

void setup() {
    auto f1 = [](int number) { Serial.println(number); };
    LambdaTest t(f1);

    t.callLambda(123);
}

void loop() {
}

And here is the related TestLambda.h content:

#include <functional>

class LambdaTest {
  public:

  LambdaTest(std::function<void (int n)> lambda){
    lambda_ptr = &lambda ;
  }

  void callLambda(int value) {
    (*lambda_ptr)(value);
  }

  protected:
    std::function<void (int n)> *lambda_ptr;

};

This example compiled just fine for a ESP32 – but when I tried to compile for a Arduino Nano, I was getting the error TestLambda.h:1:10: error: functional: No such file or directory. As a conclusion we can’t use std::function on Arduino Boards!

The following alternative however was compiling w/o issue:

typedef void (*func)(int n);

class LambdaTest {
  public:

  LambdaTest(func lambda){
    lambda_func = lambda ;
  }

  void callLambda(int value) {
    (*lambda_func)(value);
  }

  protected:
    func lambda_func;

};