How come `MyClass.MyStaticMethod()` doesn't work, but `Serial.begin()` does?

Question

MyProject.ino:

#include "MyClass.h"
void setup()
{
 Serial.begin(9600);
 // MyClass.MyStaticMethod();
 MyClass::MyStaticMethod();
}

Both uncommented lines work, but the commented (when uncommented, of course) results in this error: expected unqualified-id before '.' token.

Now, I know this is because of the incorrect scope-resolution. Yet, how come Serial manages to call static functions without the need to use :: to correction to scope-resolution.

How come MyClass.MyStaticMethod() doesn't work, but Serial.begin() does?

Answer 1

. is used to call a method on a class instance whereas :: is used to call a static method within a class itself.

There is no Serial class - Serial is merely an instance of the HardwareSerial class.

#if defined(UBRRH) && defined(UBRRL)
 HardwareSerial Serial(&UBRRH, &UBRRL, &UCSRA, &UCSRB, &UCSRC, &UDR);
#else
 HardwareSerial Serial(&UBRR0H, &UBRR0L, &UCSR0A, &UCSR0B, &UCSR0C, &UDR0);
#endif

If you want to use . then you have to instantiate your class and not use a static method:

class MyClass {
 static void myStaticMethod() {
 }
 void myMethod() {
 }
};
MyClass Fred;
// ... 
Fred.myMethod();
MyClass::myStaticMethod();

• Fine Man: Ah. That was quite the misnomer since instances are usually with a lower case. I thought it was a class. :)
• Majenko: That is the normal way, yes - but since when have Arduino done things normally? ;)
• Fine Man: If a newcomer (myself) is just beginning to see abnormalities, I can't imagine how many you've found. :)