The Basics

• Types
  Int, Double, Float, Bool (true/false), String
  Array, Set, Dictionary
  Tuples, Optionals
• Type Annotation
  let message: String = "Hello"
  var count: Int = 10
• String Interpolation
  var message = "Good"
  print("The food tastes (message).")
• Int
  Int is preferred.
  signed/unsigned
  Int8(-128~127)/Int16/Int32/Int64
  UInt8(0~255)/UInt16/UInt32/UInt64
• Floating Point
  Double is preferred.
  Float: 32bit
  Double: 64bit
• Type Inference

Swift is a type safe language.

  let pi = 3.14 //Double

• Type Conversion

Conversions between integer and floating-point numeric types must be made explicit

  var a: Int8 = 3
  var b: Int64 = Int64(a) //Using initializer

Literals:
let a: Int = 1
let b: Double = 3.14
var c: Double = a + b //error
var d: Double = (Double)a + b //right
let e: Double = 1 + 3.14 //right, literals can be added directly

• Type Alias
  typealias MyType = Int

• Tuples
  let status: (Int, String) = (200, "Ok")
  let statusCode = status.0
  let statusMsg = status.1

  var (code, msg) = status
  print(code) //200
  print(msg) //OK
  
  let status2 = (code: 200, msg: "OK")
  print(status2.code)
  print(status2.msg)
  

• Optionals
  var s: String = "Hello"
  var number: Int? = Int(s) //number may be nil

  var str: String? //str is automatically set to nil
  str = "World"
  print("The String is \(str!).") // Forced unwrapping
  

• Optional Binding
  var numString: String = "123abc"
  if let num = Int(numString) {
  print("Can convert.")
  }
  else {
  print("Can not convert.")
  }
  Multiple binding:
  if let var1 = opt1, var2 = opt2 {
  //TODO
  }

• Implicitly Unwrapping Optionals
  let str1: String? = "Optional string."
  print((str1!)) //forced unwrapping, requires an exclamation mark

  let str2: String! = "Another optional string."
  print(str2) //No need for exclamation mark
  

• Error Handling
  func mayThrow() throws {
  //logic
  }

  do {
      try mayThrow()
   }
  catch SomeError1 {
       //error handling 1
  }
  catch SomeError2{
       //error handling 2
  }
  

• Assertions
  let age: Int = 17
  assert(age>=18, "The age must be at least 18 years old.") // app will be terminated.