Creating a library: Using classes or not?

Projects Programming
22

One other option for an OOP solution even when there will only be one object instantiated is to force that object to be a Singleton. This gives you the nice encapsulation and abstraction of a class and ensures that the user won't be mucking about in your namespaces. The example below is a variant on the technique @PieterP posted here. The library provides a single instance of the class. Because the constructor is private, and the copy-constructor and operator= are deleted, it's impossible for the user to instantiate any others.

MySingletonClass.h:

#ifndef MYSINGLETONCLASS_H_
#define MYSINGLETONCLASS_H_

#include "Arduino.h"

class MySingletonClass {
public:
	MySingletonClass(const MySingletonClass &) = delete; // no copying allowed
	MySingletonClass &operator=(const MySingletonClass &) = delete; // no assignment allowed
	static MySingletonClass &getInstance(); // Accessor for singleton instance

	void examplePublicInstanceFunction();
	static void examplePublicClassFunction();

	uint8_t examplePublicInstanceVariable {0};
	static uint8_t examplePublicClassVariable;

private:
	MySingletonClass();  // Constructor is private
	void examplePrivateInstanceFunction();
	static void examplePrivateClassFunction();

	uint8_t examplePrivateInstanceVariable {0};
	static uint8_t examplePrivateClassVariable;
};

extern MySingletonClass &singleton;

#endif /* MYSINGLETONCLASS_H_ */

MySingletonClass.cpp:

#include "MySingletonClass.h"

uint8_t MySingletonClass::examplePrivateClassVariable { 0 };
uint8_t MySingletonClass::examplePublicClassVariable { 0 };

MySingletonClass::MySingletonClass() {  // Private constructor
}

MySingletonClass & MySingletonClass::getInstance() {
  static MySingletonClass instance;
  return instance;
}

void MySingletonClass::examplePublicInstanceFunction() {
}

void MySingletonClass::examplePublicClassFunction() {
}

void MySingletonClass::examplePrivateInstanceFunction() {
}

void MySingletonClass::examplePrivateClassFunction() {
}

MySingletonClass &singleton {MySingletonClass::getInstance()};

The main .ino file uses the one (and only possible) instance of the class named "singleton":

#include "Arduino.h"

#include "MySingletonClass.h"

void setup() {
	singleton.examplePublicClassVariable = 100;
	singleton.examplePublicInstanceVariable = 200;

	singleton.examplePublicInstanceFunction();
	singleton.examplePublicClassFunction();
}

void loop() {
}