error: use of 'this' in a constant expression in Arduino Class

i am trying to write a class for an arduino projekt, i am using the information in http://paulmurraycbr.github.io/ArduinoTheOOWay.html as a guide.

I want to set up a lighstrip for further use and constantly keep getting the errormessage: error: use of 'this' in a constant expression.

My code looks like this:

#include <FastLED.h>

#define LED_STRIP_PIN 2
#define LED_STRIP_NUM_LEDS 10

//const unsigned char LED_STRIP_PIN = 2;
//const int LED_STRIP_NUM_LEDS = 10;

CRGB leds[LED_STRIP_NUM_LEDS];

class LedStrip {
  unsigned char  pin;

  public:
    LedStrip(unsigned char attachTo) :
      pin(attachTo)
    {
    };

    void setup() {
      FastLED.addLeds<NEOPIXEL, pin>(leds, 10);
    };

};

//LedStrip ledstrip(LED_STRIP_PIN, LED_STRIP_NUM_LEDS);
LedStrip ledstrip(LED_STRIP_PIN);

void setup() {

}

void loop() {

}

I have tried reading up on what might cause this error, but frankly i do not understand any of it. As far as i have understood it seems like i cannot use a const there (which i am not, i think) since it might be modified during code execution.

the complete error looks like thissketch_feb03b.ino: In member function 'void LedStrip::setup()':

sketch_feb03b:20:33: error: use of 'this' in a constant expression

       FastLED.addLeds<NEOPIXEL, pin>(leds, 10);

                                 ^~~

Solution

Your issue is that pin is not a compile-time constant, and all template arguments must be compile-time constants.

There might be other options, but the (probably) easiest one is passing pin as template argument itself:

template<int pin> // make sure type of pin is correct, I don't know what addLeds expect
class LedStrip {
  public:
    LedStrip() //not really needed now
    {
    };

    void setup() {
      FastLED.addLeds<NEOPIXEL, pin>(leds, 10);
    };
};

Usage:

//if LED_STRIP_PIN is a compile-time constant, i.e. a macro or a const(expr) value
LedStrip<LED_STRIP_PIN> ledstrip;

//if LED_STRIP_PIN  is obtained at runtime, you cannot it use it at all.
LedStrip<7> ledstrip;