Do you remember issue of implicitly captured self in block and reference cycle in Objective-C?

// implicit self reference
    name = @"name";

// Fixed version 
__weak typeof(self)weakSelf = self;
    __strong typeof(weakSelf)strongSelf = weakSelf; = @"name";

In swift this is fixed now. This is the code

{[unowned self] newName in = newName
  1. All reference to self in a closure must be explicit. You will see this compiler error -
    reference to property 'name' in closure requires explicit 'self.' to make capture semantics explicit
  2. Capture list We can declare what object should be weak or unowned in the closure. The syntax is
    [ /*reference type*/ /*object*/, ... ]

Documentation about ARC and Resolving Strong reference cycle
You can find more in WWDC 2014 - Intermediate Swift