Composition, how many instances?

If I have something like:

package {
    public class Main() {
        public function Main() {
            var foo = new 开发者_运维技巧Foo();
            var bar = new Bar(foo);
        }
    }
}

package {
    public class Foo() {
        public function Foo() {

        }

        public function doSomething() {
            trace("hello");
        }
    }
}

package {
    public class Bar(foo:Foo) {
        foo.doSomething();
    }
}

How many instances of "foo" do I have?

Like, do I just have one instance that "Main" and "Bar" share? Or do I actually have two instances?

You have one instance that Main and Bar share. Objects are passed by reference; to create a new Foo you would actually have to write "new Foo()" in Bar.