Upp::Function is wrapper to represent callable operation. It is similar to std::function with two differences:

- Calling empty Function is allowed (and NOP). Returns zero.
- Functions can be combined (chained) using operator<<

#include <Core/Core.h>

using namespace Upp;

struct Foo {
	Event<int, int> WhenAddition;
	void DoAddition(int a, int b) { WhenAddition(a, b); }
};

CONSOLE_APP_MAIN
{
	StdLogSetup(LOG_COUT);
	
	// I am explicitly specifying the type here for educational purpose.
	// Normally you can simply use auto, where it is proper.
	Event<int, int> Addition = [=](int a, int b) {
		LOG("Foo::DoAddition: " << a + b);
	};
	
	Gate<int, int> Subtraction = [=](int a, int b) {
		return a - b > 0;
	};
	
	Function<int(int, int)> Multiplication = [=](int a, int b) {
		return a * b;
	};
	
	Foo myfoo;
	myfoo.WhenAddition = pick(Addition); 
	
	int a = 10, b = 5;
	
	myfoo.DoAddition(a, b);
	
	if(Subtraction(a, b))
		LOG("a is greater than b");
	
	LOG(Multiplication(a, b));
}