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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 { 
   "­🎂" 
 } 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)"
Switches: support any kind of data and variety of compar­isons
After executing the code inside the switch case that matched, program exits from the switch statement. Execution doesn't continue to the next case, so you don't need to explicitly break out of the switch at the end of each case's code.
 
let perfume = "Eau Rose" 
 switch perfume { 
 case "­Ele­ctric Cherry­": 
   print(­"­Jasmine sambac, ambret­tolide musk") 
 case "On a Date", "Born In Roma": 
   print(­"­These have a black currant note.") 
 case let x where x.hasS­uff­ix(­"­ros­e"): 
   print(­"Is it a fragrance with \(x)?") 
 default: 
   print(­"A delicious choice.") 
 } 
 // Prints "Is it a fragrance with rose?" 
for-in
: Use to iterate over items in a dict by providing pair of names for each key-value pair.
 
 let intere­sti­ngN­umbers = [ 
   "­country codes from my holida­ys": [66, 1, 86, 82, 45], 
   "­cricket player­s": [49, 56, 26, 30], 
 ] 
 
 var largest = 0 
 for (_, numbers) in intere­sti­ngN­umbers { 
   for number in numbers { 
     if number > largest { 
       largest = number 
     } 
   } 
 }