C++ Code in function as argument

Question

I have this code:

void longitudeChanged() {
  Serial.println("Longitude: " + String(GpsLon.value,8));
}

in main:

  GpsLon.onUpdate(longitudeChanged);

I would like to do something like this:

GpsLon.onUpdate({
  Serial.println("Longitude: " + String(GpsLon.value,8));
});

(Like I do in Java script!); but this is not the rigth way. How to do it?

Tnx

Erik

Answer 1

Behold, the mighty lambda!

#include <iostream>

template <typename T>
void myFunction(T t) {
    t();
}

int main() {
    myFunction([](){ std::cout << "Hi!" << std::endl; });
}

If you'd like to learn more about them, take a look here

To decrypt this a little, here's a breakdown:

• You have a function that takes another function via a template argument.
• That function does nothing other than call its argument.
• Inside of main, you call that function with a lambda as its argument.
• The lambda can be broken into three parts [] (the capture, don't worry too much about that for now) () the function arguments, in this case there are none) and { ... } (the body, just like any other function).

So the lambda part is just this:

[](){ std::cout << "Hi!" << std::endl; }

Here's another example of a lambda that takes an int and returns double its value:

[](int value){ return value * 2; }