WWDC 15 Session 106 学习笔记

Chris Lattner 實在是太帥了！

Session 106 - What’s new in swift

Why Swift 2

Fundamentals: Refine language and tools fundamentals
Safety: Affordances for writing robust and safe code
Beauty: Enable expressive libraries and APIs

用更好的語言寫更加安全和漂亮的代碼！

What’s New in Swift 2

Fundamentals
Pattern Matching
Availabilty Checking
Protocol Extensions
Error Handling

Fundamentals

Enums
```
  enum Animals {
  	case a, b
  }
```

Associated Values in Enums

  enum Either<T1, T2> {
  	case First(T1)
      case Second(T2)
  }

Recursion Enums

  enum Tree<T> {
  	case Leat(T)
  	indirect case Node(Tree, Tree)
  }

do Statement

  do {
  	let a = Animals.Troll
  	...
  }
  // loop
  repeat {
      ...
  }

Option Sets

  [option1, option2]

Defining an Option: Using Protocol-Oriented Programming
```
  struct MyFontSyle : SetOptionSetType
```

Functions and Methods
- Consistent Argument Labels
- Duplicate first name
- Underscore to disable name labels
- # argument syntax
Diagnostics
SDK Improvements
- Nullability qualifiers
- Objective-C typed Collections
Testing
```
  @testable
  import MyApp
```
Rich Comments
A Lot More!

Pattern Matching

if-let Statment

Compound Conditions

Early Exits: guard Statement

    guard let name = json["name"] as? String else {
        return .Second("missing name")
    }
    // Compound Condidtions
    guard let name = json["name"] as? String,
          let year = json["year"] as? Int else {
        return .Second("bad input")
    }

Switch

  if case .MyEnumCase(let value) = bar() where value != 42 {
  	doSomething(value)
  }

for ... in Filtering

  for value in mySequence where value != "" {
  	doSomething(value)
  }

Availabilty Checking

New APIs
- springLoaded
- old: respondsToSeletor Method
- new: get a diagnostic
- Example:
```
  if #available(OSX 10.10.3, *) {
  	...
  }
```

Protocol Extensions

Extensions

Old

  extension Array {
      func countIf(match: Element -> Bool) -> Int {
          var n = 0;
          for value in self {
              if match(value) {
                  n++;
              }
          }
          return n
      }
  }   + Global Functions

New
```
  extension CollectionType
```

Method
```
  .map().filter()
```

Error Handling

Kinds
- Trivial Errors
- Logic Errors
- Detailed, recoverable Errors

Example

try Keyword
throws Keyword

do-catch Block

  do {
      ...
  } catch let error {
  	...
  } catch {
  	fatalError()
  }

try! Keyword

Enums as Error Types

  enum DataError : ErrorType {
  	case MissingName
      case MissingFile
  }

Defer Actions

  defer { delegate?.didEndProcessing() }