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Swift Cheat Sheet (DRAFT) by

Swift beginner cheat sheet from swift docs

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Simple Values

let
for constants; 
var
for variables
Constants: value doesn't need to be known at compile time, but must assign it a value exactly once
Rule for types: constant or variable must have the same type as the value you want to assign it.
Inferring Types: Type can be inferred if value provided when creating consta­nt/var.
Specifying types: Write after the variable, separated by colon
 
let explic­itD­ouble: Double = 70
Values are never implicitly converted to another type. If conversion required, must be done explicitly
 
let lottoS­tring = "­Today's winning lotto number is " 
 let lottoN­umber = 94
 let lottoS­entence =  lottoS­tring + String­(lo­tto­Number)
Backslash string interp­olation
 
let friend­Count = 2
let friend­Cou­ntS­tring = "I have \(frie­ndC­ount) number of 
 friend­s."
Use three double quotation marks for strings that take up multiple lines.
Create arrays and dictio­naries using brackets, and access their elements by writing the index or key in brackets.
 
var toys = ["la­bub­u", "­sim­ski­", "furby"]
 toys[1] = "­fug­gle­r" 
 toys.a­ppe­nd(­"­jel­lyc­at") 
 var bestIt­emO­fThing = [ "­summer fruit" : "­man­go",] 
 bestIt­emO­fTh­ing­["summer fruit"] = "­pea­ch"
Arrays grow automa­tic­ally.
For empty array, write 
excell­ent­Fruits = []
. For an empty dictio­nary, write 
medioc­reF­ruits = [:]
.
If assigning empty array or dict to new var, you need to specify type.
 
let arrayO­fGo­odC­off­eeC­afes: [String] = [] 
 let dictCa­fes­Wit­hMa­tch­aAn­dRa­tings: [String: Float] = [:]
 

Control Flow

Condit­ionals: 
if
, 
switch
Loops: 
for-in
, 
while
, 
repeat - while
Parent­heses around condit­ion­/loop variable are optional, braces are required
 
let croiss­ant­Scores = [1.2, 2.3, 2.2, 4]
 for score in croiss­ant­Scores { 
     if score > 2.5 { 
       print(­"­Great croiss­ant­!!") 
     } 
 }
In 
if
statement, condit­ional must be a boolean expres­sion. 
if score { ... }
is an error, not implicit comparison to zero.
You can assign if conditions to an assignment
 
 let scoreD­eco­ration = if teamScore > 10 { 
   "­đźŽ‚" 
 } else { 
   "­" 
 } 
 print(­"­Sco­re:­", teamScore, scoreD­eco­ration)
Optionals: either contains a value or contains 
nil
to indicate a value is missing. A question mark after type of value marks it as optional.
 
var option­alS­tring: String? = "­Hel­lo" 
 print(­opt­ion­alS­tring == nil) 
 // prints "­fal­se"
Use 
if
and 
let
to work with missing values. If optional value is 
nil
, condit­ional is false and code in braces is skipped. Otherwise, optional value is unwrapped and assigned to constant after 
let
, which makes the unwrapped value available inside block of code.
 
var option­alName: String? = "Big Dog" 
 var greeting = "­Hel­lo!­" 
 if let name = option­alName { 
   greeting = "­Hello, \(name­)" 
 } else { 
      greeting = "­Wow­!" 
 } 
??
operator: If optional value missing, default value used instead
 
let holida­yInNov: String? = nil 
 let holida­yInDec: String = "­Bal­i" 
 let welcomeMsg = "­Enjoy \(holi­day­InNov ?? holida­yIn­Dec­)"