Updating an Array that belongs to one class from another class - arrays

Question

I'm wrote this code a long time ago and thought I understood it at that time but now I'm trying to wrap my head around how it works...
// Main.as
package {
public class Main {
public function Main() {
var fruit:Array = [];
UpdateClass.update(fruit);
trace(fruit); // Traces out the string pushed into it? How??? I think the data would've got lost...
}
}
}
// UpdateClass.as
package {
public class UpdateClass {
public static function update(array:Array):void {
array.push("haha, this is not a fruit!");
}
}
}
I just don't understand how the UpdateClass manages to update Main's fruit array? I'm thinking the data would get lost because it is not returning the new array?... When I try this with Strings and Numbers the data does get lost like expected.
I don't know what I was on when I wrote this but I would like to try and understand the logic behind this.
Thank you.

Answer 1

String and Number are "primitive" data types in AS3, while Array and other objects like MovieClip are "complex" or "reference" data types.
When you pass a primitive, its value is copied, so modifying that doesn't affect the original. When you pass a complex object, it's actually a reference to the object's address in memory, so your function is modifying the original object.

Answer 2

I'm assuming something like following when you say that the value was lost with String and Number:
// UpdateClass.as
package {
public class UpdateClass {
public static function update(num:Number):void {
num = 1;
}
}
}
The reason it was lost was because you got a reference to the original object as num. But the function update changed that reference to another Number object which contained the value '1'. This would be true for array too, if you assign another array to the passed reference like:
// UpdateClass.as
package {
public class UpdateClass {
public static function update(array:Array):void {
array = new Array();
array.push("haha, this is not a fruit!");
}
}
}
But, since you are just calling a method on the passed reference (push), 'array' still refers to the original Array and updates it.