View source for Swift Intermediate

=Intermediate Swift=
Reference
[[https://developer.apple.com/videos/wwdc/2014/?id=402 WWDC Link]]
==Optional Type==
<pre class="brush:c">
var optionalNumber = Int?
//default init to nil
optionalNumber = 9
</pre>
Non-optional type cannot be nil<br>

<h4>Example</h4>
<pre class="brush:c">
func findIndexOfArray(needle: String, array: String[]) => Int? {
  for (index, value) in enumerate(array) {
    if value == needle {
      return index
    }
  }
  return nil
}
var neighbors = ["Alex", "Anna", "Madison"]
let index = findIndexOfArray("Alex", neighbors)
if index {
  println("Found \(neighbors[index!])") // noticing the !. The ! will unwrapping the value. Must check non-nil it before unwrap.
}
//Optional binding: Check and unwrap at same time
if let indexValue = findIndexOfArray("Alex", neighbors) {
  println("Found \(neighbors[indexValue])")
}
</pre>
<h4>Optional Chaining</h4>
Example Without Chaining: <br>
<pre class="brush:c">
var addressNumber: Int?
if let home = paul.residence {
  if let postalAddress = home.Address {
    if let building = postalAddress.buildingNumber {
      if let convertedNumber = building.toInt() {
        addressNumber = converttedNumber
      }
    }
  }
}
</pre>
With Chaining<br>
<pre class="brush:c">
addressNumber = paul.residence?.address?.buildingNumber?.toInt()
//addressNumber is still an optional value at this state
//Combine again
if let addressNumber = paul.residence?.address?.buildingNumber?.toInt() {
  addtoDb("paul", addressNumber)
}
</pre>

<h4>Optionals Under the Hood</h4>
<pre>
enum Optional<T> {
  case None
  case Some(T)
}
</pre>

==Automatic Reference Counting==
<h4>Weak References</h4>
Use Weal references among objects with independent lifetimes<br>
weak references are optionals
If part of the object goes away, the other objects stay
<h4>Unowned References</h4>
Use Unowned references from owned objects with the same lifetime<br>
If part of the object goes away, the entire object go away

==Initialization==
Every value '''MUST''' be initialized before it is used