swift4: deeper dive- types

Currently enrolled in Udemy’s- The Complete iOS 11 & Swift Developer Course Notes from Lesson 4

What is Swift?

Notes from Apple’s Swift 4 Developer page

• used to develop iOS, macOS, watchOS, and tvOS
• released in 2014 and is open source
• built with the LLVM compiler
• easy to learn:
  • interactive and fast feedback with Swift Playgrounds & REPL (Read, Eval, Print, Loop) in Xcode
• designed for safety
  • automatic memory management
  • type safety
  • null safety

Using var vs let

• var is to indicate that the variable’s value may change over it lifetime
• let is to indicate that the variable’s value may NOT change over its lifetime
• best practice is to use let whenever possible, because it prevents unintended value changes

Type Conversions

• can convert types into other types by Type(yourVariable)
• e.g.

  let myFloat1 = 9.02 
  print(String(myFloat1))
  

• can explicity declare the types of variables
  • helpful when you want to declare an array of doubles, but not give them decimal values
    • e.g.

      var myDouble: [Double] = [1,2,3]
      //these are actually doubles [1.0, 2.0, 3.0]
      

Arrays

• cool things to note:
  • although not recommended, can have mix typed arrays, where its type is Any
    • example: let mixArray: Any = ["hey", 0, false]
  • initializing an empty array of a type: let stringArray = [String]()

Dictionaries

• syntax of a dictionary;
  • let dictionary = ["key": "value"]
• optionals are returned when retrieving a value from a dictionary as a default :
  • print(dictionary["key"])
• or can force unwrap it and return the raw value, if you know for certain that they key exists:
  • print(dictionary["key"]!)