Declare simple value

• let is constant
• var is mutable variable

Primitive Types

let i = 42 // An Int type

let s = "hello" // A String type

let s2: String = "Declare with explicit type"

Class & Struct

• Create your own type using class or struct

struct Person {
    let name: String
    let birthYear: Int
}

let alice = Person(...) // alice is an instance 

Class vs Struct

• Reference type vs Value type
• Struct will be copied when passed or assigned
• Struct property needs to state mutability
• Use struct for data model
• Class are passed by "pointers" reference
• Class has inheritance (object oriented programming)

Enum

• A simple type with certain known enumerations

Array

• The simplest and most widely used collection type
• Others are dictionary, set

Control Flow

• if-let-else
• switch-case
• while

Loops

• for item in array
• for i in 0..<10

Functions

• Operation with input and output

func isEven(num: Int) -> Bool {
    ...
}

Function as type, closure

• (Int) -> Bool
• Array has many methods that accepts closure