You can write the value of this a file:

 var entityID : String;

But this has no implicit value when you try to write it to a file:

 var entity : Entity;

Obviously there are ways to make Entity serializable, but as a reference, it is not inherently so.

I wanted to ask you if you could clarify something:

“…but the important thing to remember is that we can’t serialize references, but we can serialize IDs. Serializing forms a critical component of load/save systems and networked games so we’re going to lay the foundation as we proceed.”

Can you explain what you mean by “we can’t serialize references”? By serialize, what specifically do you mean, and how are we prevented from serializing references (in AS3, I presume you mean)?

By the way, you may want to check out something I’ve been doing in relation to entities, using factories and composition rather than inheritance for entity construction:

http://www.visualharmonics.co.uk/actionscript-3/using-function-closures-in-object-composition/

Actually I’m using your entity code as a bit of a reference, although due to the discrete MVC nature of my framework, there is a quite a big difference in how additions and removals are handled.

A quick question on your EntityContainer::tick() method:

public function tick( a_deltaTime : Number ) : void
{       
    var entityCount : int = m_entities.length;
    for( var entityIndex : int = entityCount - 1; entityIndex >= 0; entityIndex-- )
    {
        var entity : IEntity = m_entities[ entityIndex ];
        entity.tick( a_deltaTime );
    }

    processAddAndRemoves();
}

Why have you used a reverse count to iterate through entities to tick()?

Thanks,

-Nick