Swift Keywords
This post is brought to you by Emerge Tools, the best way to build on mobile.
It’s been said before and it’ll be mentioned again, a craftsmen is as only as good as their tools of the trade. Our strict adherence to such tools take us where we want to go or make the thing we’ve dreamed of.
And I don’t say that in a pejorative sense, since there is always more to learn. So today — we’ll look at every single keyword Swift (version 5.5) has to offer us along with some code for each one, all in the name of booking up on our trade’s tools.
Some are obvious, some are obscure and some are sorta(ish) recognizable but they all make for great reading and learning. This one is long, ready?
Lets.Dance(.rightNow)
Declaration Keywords
associatedtype: Gives a placeholder name to a type that is used as part of a protocol. The type is not specified until the protocol is adopted.
protocol Entertainment
{
associatedtype MediaType
}
class Foo : Entertainment
{
typealias MediaType = String // Could be any type to fit the need
}
class : A general-purpose, flexible construct that become the building blocks of your program’s code. Similar to struct, except that:
- Inheritance enables one class to inherit the characteristics of another.
- Type casting enables you to check and interpret the type of a class instance at runtime.
- Deinitializers enable an instance of a class to free up any resources it has assigned.
- Reference counting allows more than one reference to a class instance.
class Person
{
var name:String
var age:Int
var occupation:String
}
deinit: Called immediately before a class instance is deallocated.
class Person
{
var name:String
var age:Int
var occupation:String
deinit
{
//Deallocated from the heap, tear down things here
}
}
enum : Defines a common type for a group of related values and enables you to work with those values in a type-safe way within your code. In Swift, they are first-class types and can use features typically supported only by classes in other languages.
enum Difficulty
{
case easy
case medium
case hard
}
extension : Lets one add new functionality to an existing class, structure, enumeration, or protocol type.
class Person
{
var name:String = ""
var age:Int = 0
var occupation:String = ""
}
extension Person
{
func printInfo()
{
print("My name is (name), I'm (age) years old and I'm a (occupation).")
}
}
fileprivate : An access control construct that restricts scope to only the defining source file.
// Person is only accessible in the file it's defined in.
fileprivate class Person
{
var jobTitle:String = ""
}
extension Person
{
//This wouldn't compile using "private"
func printJobTitle()
{
print("My job is (jobTitle)")
}
}
func : Self-contained chunks of code that perform a specific task.
func addNumbers(num1:Int, num2:Int) -> Int
{
return num1+num2
}
import : Exposes a framework or application that is built and shipped as a single unit into the given binary.
import UIKit
//All of UIKit's code is now available
class Foo {}
init : The process of preparing an instance of a class, structure, or enumeration for use.
class Person
{
init()
{
//Set default values, prep for use, etc.
}
}
inout : A value that is passed to a function and modified by it, and is passed back out of the function to replace the original value. Applies to both reference and value types.
func dangerousOp(_ error:inout NSError?)
{
error = NSError(domain: "", code: 0, userInfo: ["":""])
}
var potentialError:NSError?
dangerousOp(&potentialError)
//Now potentialError is no longer nil and initialized
internal : An access control construct that allows entities to be used within any source file from its defining module, but not in any source file outside of it.
class Person
{
internal var jobTitle:String = ""
}
let aPerson = Person()
aPerson.jobTitle = "This can set anywhere in the application"
let : Defines a variable as immutable.
let constantString = "This cannot be mutated going forward"
open : An access control construct that allows objects to be both accessible and subclassable outside of its defining module. For members, they are both accessible and overridable outside of its defining module.
open var foo:String? //This can be overriden and accessible inside and outside of the app. Writing frameworks is a common use case for this access modifier
operator : A special symbol or phrase that you use to check, change, or combine values.
//The "-" unary operator decrements a single target
let foo = 5
let anotherFoo = -foo //anotherFoo now equals -5
//The "+" binary operator combines two values
let box = 5 + 3
//The "&&" logical operator combines two boolean values
if didPassCheckOne && didPassCheckTwo
//The ternary conditional operator considers three values
let isLegalDrinkingAgeInUS:Bool = age >= 21 ? true : false
private : An access control construct that allows entities to be scoped to its defining declaration.
class Person
{
private var jobTitle:String = ""
}
extension Person
{
//This won't compile, jobTitle is only available inside of Person
func printJobTitle()
{
print("My job is (jobTitle)")
}
}
precedencegroup : Defines an operator’s precedence in relation to other infix operators along with its associativity.
precedencegroup StringJoinedPrecedence {
higherThan: AssignmentPrecedence
}
infix operator ~== : StringJoinedPrecedence
func ~== (lhs: String, rhs: String) -> String {
return lhs + rhs
}
var foo: String = "Join me"
foo ~== " on the dark side."
// Foo now equals 'Join me on the dark side.'
protocol : Defines a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality.
protocol Blog
{
var wordCount:Int { get set }
func printReaderStats()
}
class SwiftjectiveCPost : Blog
{
var wordCount:Int
init(wordCount:Int)
{
self.wordCount = wordCount
}
func printReaderStats()
{
//Print out some stats on the post
}
}
public : An access control construct that allows objects to be both accessible and subclassable but only inside of its defining module. For members, they are both accessible and overridable inside of its defining module.
public var foo:String? //This can be overriden and accessible anywhere inside of the app, but not outside of it.
static : Defines methods that are called on the type itself. Also used to define static members.
class Person
{
var jobTitle:String?
static func assignRandomName(_ aPerson:Person)
{
aPerson.jobTitle = "Some random job"
}
}
let somePerson = Person()
Person.assignRandomName(somePerson)
//somePerson.jobTitle is now "Some random job"
struct : A general-purpose, flexible construct that become the building blocks of your program’s code and can also provide member wise initializers. Unlike a class, they are always copied when they are passed around in your code and as such, do not use automatic reference counting. In addition, they do not
- Use inheritance.
- Allow type casting at runtime.
- Have, or use, deinitializers.
struct Person
{
var name:String
var age:Int
var occupation:String
}
subscript : A shortcut for accessing the member elements of a collection, list, or sequence.
var postMetrics = ["Likes":422, "ReadPercentage":0.58, "Views":3409]
let postLikes = postMetrics["Likes"]
typealias : Introduces a named alias of an existing type into your program.
typealias JSONDictionary = [String: AnyObject]
func parseJSON(_ deserializedData:JSONDictionary){}
var : Defines a variable as mutable.
var mutableString = ""
mutableString = "Mutated"
Keywords in Statements
break : Ends program execution of a loop, an if statement, or a switch statement.
for idx in 0...3
{
if idx % 2 == 0
{
//Exits the loop on the first even value
break
}
}
case : A statement that is evaluated and then compared with the provided patterns inside a switch case.
let box = 1
switch box
{
case 0:
print("Box equals 0")
case 1:
print("Box equals 1")
default:
print("Box doesn't equal 0 or 1")
}
continue : Ends program execution of the current iteration of a loop statement but does not stop execution of the loop statement.
for idx in 0...3
{
if idx % 2 == 0
{
//Immediately begins the next iteration of the loop
continue
}
print("This code never fires on even numbers")
}
default : Used to cover any values that are not addressed explicitly in a case.
let box = 1
switch box
{
case 0:
print("Box equals 0")
case 1:
print("Box equals 1")
default:
print("Covers any scenario that doesn't get addressed above.")
}
defer : Used for executing code just before transferring program control outside of the scope that it appears in.
func cleanUpIO()
{
defer
{
print("This is called right before exiting scope")
}
//Close out file streams,etc.
}
do : Begins a statement to handle errors by running a block of code.
do
{
try expression
//statements
}
catch someError ex
{
//Handle error
}
else : Used in conjunction with an if statement, it executes one part of code when the condition is true and another part of code when the same condition is false.
if val > 1
{
print("val is greater than 1")
}
else
{
print("val is not greater than 1")
}
fallthrough : Explicitly allows execution to continue from one case to the next in a switch statement.
let box = 1
switch box
{
case 0:
print("Box equals 0")
fallthrough
case 1:
print("Box equals 0 or 1")
default:
print("Box doesn't equal 0 or 1")
}
for : Iterates over a sequence, such as ranges of numbers, items in an array, or characters in a string. *pairs with the __in_ keyword_
for _ in 0..<3 { print ("This prints 3 times") }
guard : Used to transfer program control out of a scope if one or more conditions aren’t met, while also unwrapping any optional values provided.
private func printRecordFromLastName(userLastName: String?)
{
guard let name = userLastName, userLastName != "Null" else
{
//Sorry Bill Null, find a new job
return
}
//Party on
print(dataStore.findByLastName(name))
}
if : Used for executing code based on the evaluation of one or more conditions.
if 1 > 2
{
print("This will never execute")
}
in : Iterates over a sequence, such as ranges of numbers, items in an array, or characters in a string. *pairs with the __for_ keyword_
for _ in 0..<3 { print ("This prints 3 times") }
repeat : Performs a single pass through the loop block first, before considering the loop’s condition.
repeat
{
print("Always executes at least once before the condition is considered")
}
while 1 > 2
return : Immediately breaks control flow out of the current context, and additionally returns a value supplied after it if one is present.
func doNothing()
{
return //Immediately leaves the context
let anInt = 0
print("This never prints (anInt)")
}
and
func returnName() -> String?
{
return self.userName //Returns the value of userName
}
switch : Considers a value and compares it against several possible matching patterns. It then executes an appropriate block of code, based on the first pattern that matches successfully.
let box = 1
switch box
{
case 0:
print("Box equals 0")
fallthrough
case 1:
print("Box equals 0 or 1")
default:
print("Box doesn't equal 0 or 1")
}
where : Requires that an associated type must conform to a certain protocol, or that certain type parameters and associated types must be the same. It’s also used to provide an additional condition within a pattern in cases that are considered to be matched to the control expression.
let concatenatedThoughts = """
The where clause can be used in several contexts, these are examples of their primary use as a generic where clause and pattern matching.
"""
protocol Nameable
{
var name:String {get set}
}
func createdFormattedName(_ namedEntity:T) -> String where T:Equatable
{
//Only entities that conform to Nameable which also conform to equatable can call this function
return "This things name is " + namedEntity.name
}
and
for i in 0…3 where i % 2 == 0
{
print(i) //Prints 0 and 2
}
while : Performs a set of statements until a condition becomes false.
while foo != bar
{
print("Keeps going until the foo == bar")
}
Expressions and Types Keywords
Any : Can be used to represent an instance of any type at all, including function types.
var anything = [Any]()
anything.append("Any Swift type can be added")
anything.append(0)
anything.append({(foo: String) -> String in "Passed in (foo)"})
as : A type cast operator used to attempt to cast a value to a different, or an expected and specific, type.
var anything = [Any]()
anything.append("Any Swift type can be added")
anything.append(0)
anything.append({(foo: String) -> String in "Passed in (foo)" })
let intInstance = anything[1] as? Int
or
var anything = [Any]()
anything.append("Any Swift type can be added")
anything.append(0)
anything.append({(foo: String) -> String in "Passed in (foo)" })
for thing in anything
{
switch thing
{
case 0 as Int:
print("It's zero and an Int type")
case let someInt as Int:
print("It's an Int that's not zero but (someInt)")
default:
print("Who knows what it is")
}
}
catch : If an error is thrown by code in a do clause, it’s matched against a catch clause to determine how the error will be handled. *Excerpt from one of my previous posts on Swift’s error handling.
do
{
try haveAWeekend(4)
}
catch WeekendError.Overtime(let hoursWorked)
{
print("You worked (hoursWorked) more than you should have")
}
catch WeekendError.WorkAllWeekend
{
print("You worked 48 hours :-0")
}
catch
{
print("Gulping the weekend exception")
}
false : One of two constant values Swift used to represent the logical type, Bool, as not being true.
let alwaysFalse = false
let alwaysTrue = true
if alwaysFalse { print("Won't print, alwaysFalse is false 😉")}
is : A type check operator used to determine whether an instance is of a certain subclass type.
class Person {}
class Programmer : Person {}
class Nurse : Person {}
let people = [Programmer(), Nurse()]
for aPerson in people
{
if aPerson is Programmer
{
print("This person is a dev")
}
else if aPerson is Nurse
{
print("This person is a nurse")
}
}
nil : Represents a stateless value for any type in Swift.
let concatenatedThoughts = """
Different from Objective-C's nil, which is a pointer to a nonexistent object.
"""
class Person{}
struct Place{}
//Literally any Swift type or instance can be nil
var statelessPerson:Person? = nil
var statelessPlace:Place? = nil
var statelessInt:Int? = nil
var statelessString:String? = nil
rethrows : Indicates that the function throws an error only if one of its function parameters throws an error.
func networkCall(onComplete:() throws -> Void) rethrows
{
do
{
try onComplete()
}
catch
{
throw SomeError.error
}
}
self : An implicit property that every instance of a type has, which is exactly equivalent to the instance itself. Also very useful for distinguishing between a parameter name and a property name.
class Person
{
func printSelf()
{
print("This is me: (self)")
}
}
let aPerson = Person()
aPerson.printSelf() //"This is me: Person"
Self : In protocols, represents the type that will eventually conform to the given protocol.
protocol Printable
{
func printTypeTwice(otherMe:Self)
}
struct Foo : Printable
{
func printTypeTwice(otherMe: Foo)
{
print("I am me plus (otherMe)")
}
}
let aFoo = Foo()
let anotherFoo = Foo()
aFoo.printTypeTwice(otherMe: anotherFoo) //I am me plus Foo()
super : Exposes access to the superclass version of a method, property, or subscript.
class Person
{
func printName()
{
print("Printing a name. ")
}
}
class Programmer : Person
{
override func printName()
{
super.printName()
print("Hello World!")
}
}
let aDev = Programmer()
aDev.printName() //"Printing a name. Hello World!"
throw : Used to explicitly throw an error from the current context.
enum WeekendError: Error
{
case Overtime
case WorkAllWeekend
}
func workOvertime () throws
{
throw WeekendError.Overtime
}
throws : Indicates that a function, method, or initializer can potentially throw an error.
enum WeekendError: Error
{
case Overtime
case WorkAllWeekend
}
func workOvertime () throws
{
throw WeekendError.Overtime
}
//"throws" indicates in the function's signature that I need use try, try? or try!
try workOvertime()
true One of two constant values Swift used to represent the logical type, Bool, as being true.
let alwaysFalse = false
let alwaysTrue = true
if alwaysTrue { print("Always prints")}
try : Indicates that the following function could potentially throw an error. Can be used three different ways: try, try? and try!.
let aResult = try dangerousFunction() //Handle it, or propagate it
let aResult = try! dangerousFunction() //This could trap
if let aResult = try? dangerousFunction() //Unwrap the optional
Keywords Using Patterns
_ : A wilcard pattern that matches and ignores any value.
for _ in 0..<3
{
print("Just loop 3 times, index has no meaning")
}
another use
let _ = Singleton() //Ignore value or unused variable
Keywords Using #
#available: A condition of an if, while, and guard statement to query the availability of APIs at runtime, based on specified platforms arguments.
if #available(iOS 10, *)
{
print("iOS 10 APIs are available")
}
#colorLiteral: A playground literal which brings up an interactive color picker to assign to a variable.
let aColor = #colorLiteral //Brings up color picker
#column: A special literal expression that returns the column number in which it begins.
class Person
{
func printInfo()
{
print("Some person info - on column \(#column)")
}
}
let aPerson = Person()
aPerson.printInfo() //Some person info - on column 53
#dsohandle: Returns the dynamic shared object, i.e. the containing executable or dylib image, and returns it as an UnsafeRawPointer, typically used in conjunction with logging.
let context = #dsohandle
#elseif: A conditional compiler control statement that allows the program to conditionally compile some given code. Used in conjunction with an #if statement, it executes one part of code when the given condition is true.
#if os(iOS)
print("Compiled for an iOS device")
#elseif os(macOS)
print("Compiled on a mac computer")
#endif
#else: A conditional compiler control statement that allows the program to conditionally compile some given code. Used in conjunction with an #if statement, it executes one part of code when the condition is true and another part of code when the same condition is false.
#if os(iOS)
print("Compiled for an iOS device")
#else
print("Not on an iOS device")
#endif
#endif: A conditional compiler control statement that allows the program to conditionally compile some given code. Used for marking the end of conditionally compiled code.
#if os(iOS)
print("Compiled for an iOS device")
#endif
#error: Creates a build time error by the Swift compiler whenever it’s encountered.
#if API_VERSION > 4 && os(tvOS)
// Prevents project from building.
#error("Cool API Version 4 isn't supported on tvOS.")
#endif
#fileID: Returns a String with the name of the file and module it’s contained in.
let debugInfo = "Crash log created. Find it at \(#fileID) in this project's folder."
#endif
#fileLiteral: A playground literal which brings up an interactive color picker to assign to a variable.
let readme = #fileLiteral //Brings up a picker to select a file which goes inside the Playground's Resources folder
#filePath: Returns a String with the full file’s path.
let debugInfo = "Crash log created. Find it at \(#filePath)."
#file: A special literal expression that returns the name of the file in which it appears.
class Person
{
func printInfo()
{
print("Some person info - inside file \(#file)")
}
}
let aPerson = Person()
aPerson.printInfo() //Some person info - inside file /*file path to the Playground file I wrote it in*/
#function: A special literal expression which returns the name of a function, inside a method it is the name of that method, inside a property getter or setter it is the name of that property, inside special members like init or subscript it is the name of that keyword, and at the top level of a file it is the name of the current module.
class Person
{
func printInfo()
{
print("Some person info - inside function \(#function)")
}
}
let aPerson = Person()
aPerson.printInfo() //Some person info - inside function printInfo()
#if: A conditional compiler control statement that allows the program to conditionally compile some given code. Used for executing code based on the evaluation of one or more conditions.
#if os(iOS)
print("Compiled for an iOS device")
#endif
#imageLiteral: A playground literal which brings up a picker to select an image which returns as aUIImage instance.
let anImage = #imageLiteral //Brings up a picker to select an image inside the playground file
#keyPath: Returns the key, as a String, for the specified property to be used for any key-value coding APIs in Objective-C.
class Person: NSObject {
@objc var age: Int
init(age:Int) {
self.age = age
}
}
let jordan = Person(age: 33)
let ageKeyPath = #keyPath(Person.age)
let age = jordan.value(forKeyPath: ageKeyPath) // 33
#line: A special literal expression which returns the line number on which it appears.
class Person
{
func printInfo()
{
print("Some person info - on line number \(#line)")
}
}
let aPerson = Person()
aPerson.printInfo() //Some person info - on line number 5
#selector: An expression that forms the Objective-C selector which uses static checking to ensure that the method exists and that it’s also exposed to Objective-C.
//Static checking occurs to make sure doAnObjCMethod exists
control.sendAction(#selector(doAnObjCMethod), to: target, forEvent: event)
#sourceLocation: A line control statement used to specify a line number and filename that can be different from the line number and filename of the source code being compiled. Useful for changing the source code location used by Swift for diagnostic and debugging purposes.
#sourceLocation(file:"foo.swift", line:6)
//Reports new values
print(#file)
print(#line)
//This resets the source code location back to the default values numbering and filename
#sourceLocation()
print(#file)
print(#line)
#warning: Produces a warning picked up by the Swift compiler.
func login(withInfo:Info) {
#warning("This is temporary, and will be deprecated in the next seed.")
client.login(with: info)
}
Context Specific Keywords
let concatenatedThoughts = """
These keywords can actually be used as identifiers if they are used outside of their respective contexts.
"""
associativity : Specifies how a sequence of operators with the same precedence level are grouped together in the absence of grouping parentheses by using left, right or none .
infix operator ~ { associativity right precedence 140 }
4 ~ 8
convenience : Secondary, supporting initializers for a class that eventually delegate initialization of the instance to a designated initializer.
class Person
{
var name:String
init(_ name:String)
{
self.name = name
}
convenience init()
{
self.init("No Name")
}
}
let me = Person()
print(me.name)//Prints "No Name"
didSet : A property observer that is invoked immediately after a value is stored on a property.
var data = [1,2,3]
{
didSet
{
tableView.reloadData()
}
}
dynamic : Indicates that access to that member or function is never inlined or devirtualized by the compiler, which means access to that member is always dynamically dispatched (instead of statically) using the Objective-C runtime.
class Person
{
//Implicitly has the "objc" attribute now too
//This is helpful for interop with libs or
//Frameworks that rely on or are built
//Around Obj-C "magic" (i.e. some KVO/KVC/Swizzling)
dynamic var name:String?
}
final : Prevents a method, property, or subscript from being overridden.
final class Person {}
class Programmer : Person {} //Compile time error
get : Returns the given value for a member. Also used with computed properties to get other properties and values indirectly.
class Person
{
var name:String
{
get { return self.name }
set { self.name = newValue}
}
var indirectSetName:String
{
get
{
if let aFullTitle = self.fullTitle
{
return aFullTitle
}
return ""
}
set (newTitle)
{
//If newTitle was absent, newValue could be used
self.fullTitle = "(self.name) :(newTitle)"
}
}
}
indirect : Indicates that an enumeration has another instance of the enumeration as the associated value for one or more of the enumeration cases.
indirect enum Entertainment
{
case eventType(String)
case oneEvent(Entertainment)
case twoEvents(Entertainment, Entertainment)
}
let dinner = Entertainment.eventType("Dinner")
let movie = Entertainment.eventType("Movie")
let dateNight = Entertainment.twoEvents(dinner, movie)
infix : Specifies that an operator is used between two targets. If a new global operator is defined as an infix operator, it also requires membership to a precedence group.
let twoIntsAdded = 2 + 3
lazy : A property whose initial value is not calculated until the first time it is used.
class Person
{
lazy var personalityTraits = {
//Some crazy expensive database hit
return ["Nice", "Funny"]
}()
}
let aPerson = Person()
aPerson.personalityTraits //Database hit only happens now once it's accessed for the first time
left : Specifies the associativity of an operator as left-to-right so operators with the same precedence level are grouped together correctly in the absence of grouping parentheses.
//The "-" operator's associativity is left to right
10-2-4 //Logically grouped as (10-2) - 4
mutating : Allows modification of the properties of a structure or enumeration within a particular method.
struct Person
{
var job = ""
mutating func assignJob(newJob:String)
{
self = Person(job: newJob)
}
}
var aPerson = Person()
aPerson.job //""
aPerson.assignJob(newJob: "iOS Engineer at Buffer")
aPerson.job //iOS Engineer at Buffer
none : Specifies that an operator has the absence of any associativity applied to it, which restricts operators of the same precedence level from appearing adjacent to each to other.
//The "<" operator is a nonassociative operator
1 < 2 < 3 //Won't compile
nonmutating : Indicates that a member’s setter doesn’t modify the containing instance, but rather has other intended consequences.
enum Paygrade
{
case Junior, Middle, Senior, Master
var experiencePay:String?
{
get
{
database.payForGrade(String(describing:self))
}
nonmutating set
{
if let newPay = newValue
{
database.editPayForGrade(String(describing:self), newSalary:newPay)
}
}
}
}
let currentPay = Paygrade.Middle
//Updates Middle range pay to 45k, but doesn't mutate experiencePay
currentPay.experiencePay = "$45,000"
optional : Used to declare optional methods in protocols. These requirements do not have to be implemented by types that conform to it.
@objc protocol Foo
{
func requiredFunction()
@objc optional func optionalFunction()
}
class Person : Foo
{
func requiredFunction()
{
print("Conformance is now valid")
}
}
override : Indicates that a subclass will provide its own custom implementation of an instance method, type method, instance property, type property, or subscript that it would otherwise inherit from a superclass.
class Person
{
func printInfo()
{
print("I'm just a person!")
}
}
class Programmer : Person
{
override func printInfo()
{
print("I'm a person who is a dev!")
}
}
let aPerson = Person()
let aDev = Programmer()
aPerson.printInfo() //I'm just a person!
aDev.printInfo() //I'm a person who is a dev!
postfix : Specifies that an operator follows the target that it operates on.
var optionalStr:String? = "Optional"
print(optionalStr!)
precedence : Represents an operator’s higher priority than others; so that these operators are applied first.
infix operator ~ { associativity right precedence 140 }
4 ~ 8
prefix : Specifies that an operator precedes the target it operates on.
var anInt = 2
anInt = -anInt //anInt now equals -2
Protocol : Refers to the Protocol’s metatype.
protocol Foo { }
let fooMetatype: Foo.Protocol = Foo.self // fooMetatype equals Foo.Protocol
required : Enforces the compiler to make sure that every subclass of the class must implement the given initializer.
class Person
{
var name:String?
required init(_ name:String)
{
self.name = name
}
}
class Programmer : Person
{
//Excluding this init(name:String) would be a compiler error
required init(_ name: String)
{
super.init(name)
}
}
right : Specifies the associativity of an operator as right-to-left so operators with the same precedence level are grouped together correctly in the absence of grouping parentheses.
//The "??" operator's associativity is right to left
var box:Int?
var sol:Int? = 2
let foo:Int = box ?? sol ?? 0 //Foo equals 2
set : Takes in a value for a member to set as its new value. Also used with computed properties to set other properties and values indirectly. If a computed property’s setter does not define a name for the new value to be set, a default name of newValue can be used implicitly.
class Person
{
var name:String
{
get { return self.name }
set { self.name = newValue}
}
var indirectSetName:String
{
get
{
if let aFullTitle = self.fullTitle
{
return aFullTitle
}
return ""
}
set (newTitle)
{
//If newTitle was absent, newValue could be used
self.fullTitle = "(self.name) :(newTitle)"
}
}
}
some: Used to define an opaque type.
var body: some View {
// This could return any kind of View, the type must only conform to the View protocol.
}
Type : Refers to the type of any type, including class types, structure types, enumeration types, and protocol types.
class Person {}
class Programmer : Person {}
let aDev:Programmer.Type = Programmer.self
unowned : Enables one instance in a reference cycle to refer to the other instance without keeping a strong hold on it when the other instance has the same lifetime or a longer lifetime.
class Person
{
var occupation:Job?
}
//Here, a job never exists without a Person instance, and thus never outlives the Person who holds it.
class Job
{
unowned let employee:Person
init(with employee:Person)
{
self.employee = employee
}
}
weak : Enables one instance in a reference cycle to refer to the other instance without keeping a strong hold on it when the other instance has a shorter lifetime — that is, when the other instance can be deallocated first.
class Person
{
var residence:House?
}
class House
{
weak var occupant:Person?
}
var me:Person? = Person()
var myHome:House? = House()
me!.residence = myHome
myHome!.occupant = me
me = nil
myHome!.occupant //Is now nil
willSet : A property observer that is invoked right before a value is stored on a property.
class Person
{
var name:String?
{
willSet(newValue) {print("I've got a new name, it's (newValue)!")}
}
}
let aPerson = Person()
aPerson.name = "Jordan" //Prints out "I've got a new name, it's Jordan!" right before name is assigned to
Wrapping Up
Phew!
This was a fun one to author up. I picked up a few things I hadn’t really thought much of prior to writing it, but I do think the trick here is not to memorize it like a list of definitions for an exam.
Rather, keep this list handy. Let it hit your brainwaves every now and again — and when the time comes when you need that specific keyword for that outlier scenario, you’ll know it and use it.
Until next time ✌️.