Question

I’ve noticed in some of the examples ive seen that you will set a engine( class variable ) to a _engine ( ivar ). I don’t get it. What’s going on here?

Here is an example of what I’m saying:
@synthesize engine = _engine, delegate = _delegate

Answer 1

This syntax maps a property to an instance variable (ivar) with a different name.

So:

@synthesize engine = _engine;

will create property accessor methods that access the _engine ivar instead of engine. You can still access the propery as:

object.engine

More info in the Apple developer documentation on properties (section Property Implementation Directives)