Virtual Functions

Virtual functions are just func-module functions without a body, they are just declarations of functions inside a func-module:

use Core.print

func IMove:
	def move();

def main():
	print("Hello, World!\n");

This program will print this line to the console:

Hello, World!

As you can see, the compiler will compile this program just fine. But, it is not possible to call a "virtual" function directly, this will result in a compile error:

use Core.print

func IMove:
	def move();

def main():
	print("Hello, World!\n");
	IMove.move();

This program will result in this compile error:

Parse Error at main.ft:8:5
└─┬┤E0000│
6 │ def main():
8 │ »   IMove.move();
┌─┴─────┘
└─ Direct call of virtual function is not allowed

Because the virtual function does not have an body, it is not allowed to call it directly. But what wee can do, is call that virtual function on an interface instance of that func type:

use Core.print

func IMove:
	def move();

def apply(mut IMove m):
	m.move();

def main():
	print("Hello, World!\n");

This program will print this line to the console:

Hello, World!

This works because the virtual function function needs to be linked to a "real" function at the entity-composition phase when creating new entity types. We cannot call the apply function yet, because without an entity type, there is no way to create an interface instance.