All the pieces about private and non-private Swift attributes

Public attributes

Public Swift language attributes are marked with the @ image, they’re (kind of) properly documented and prepared to be used. Right here is the whole listing of all the general public Swift language attributes. Most of them will appear very acquainted… 😉

@IBOutlet

In case you mark a property with the @IBOutlet attribute, the Interface Builder (IB) will acknowledge that variable and you’ll join your supply together with your visuals by the offered “outlet” mechanism.

@IBOutlet weak var textLabel: UILabel!

@IBAction

Equally, @IBAction is an attribute that makes attainable connecting actions despatched from Interface Builder. So the marked methodology will instantly obtain the occasion fired up by the person interface. 🔥

@IBaction func buttonTouchedAction(_ sender: UIButton) {}

@IBInspectable, @GKInspectable

Marking an NSCodable property with the @IBInspectable attribute will make it simply editable from the Interface Builder’s inspector panel. Utilizing @GKInspectable has the identical conduct as @IBInspectable, however the property shall be uncovered for the SpriteKit editor UI as an alternative of IB. 🎮

@IBInspectable var borderColor: UIColor = .black
@GKInspectable var mass: Float = 1.21

@IBDesignable

When utilized to a UIView or NSView subclass, the @IBDesignable attribute lets Interface Builder know that it ought to show the precise view hierarchy. So mainly something that you simply draw inside your view shall be rendered into the IB canvas.

@IBDesignable class MyCustomView: UIView {  }

@UIApplicationMain, @NSApplicationMain

With this attribute you may mark a category as the appliance’s delegate. Often that is already there in each AppDelegate.swift file that you’re going to ever create, nevertheless you may present a primary.swift file and name the [UI|NS]ApplicationMain methodology by hand. #pleasedontdoit 😅

@out there

With the @out there attribute you may mark varieties out there, deprecated, unavailable, and many others. for particular platforms. I am not going into the small print there are some nice posts about the way to use the attribute with availability checkings in Swift.

@out there(swift 4.1)
@out there(iOS 11, *)
func avaialbleMethod() {  }

@NSCopying

You possibly can mark a property with this attribute to make a replica of it as an alternative of the worth of the property iself. Clearly this may be actually useful if you copy reference varieties.

class Instance: NSOBject {
    @NSCopying var objectToCopy: NSObject
}

@NSManaged

In case you are utilizing Core Knowledge entities (often NSManagedObject subclasses), you may mark saved variables or occasion strategies as @NSManaged to point that the Core Knowledge framework will dynamically present the implementation at runtime.

class Individual: NSManagedObject {
    @NSManaged var identify: NSString
}

@objcMembers

It is mainly a comfort attribute for marking a number of attributes out there for Goal-C. It is legacy stuff for Goal-C dinosaurs, with efficiency caveats. 🦕

@objcMembers class Individual {
    var firstName: String?
    var lastName: String?
}

@escaping

You possibly can mark closure parameters as @escaping, if you wish to point out that the worth will be saved for later execution, so in different phrases the worth is allowed to survive the lifetime of the decision. 💀

var completionHandlers: [() -> Void] = []

func add(_ completionHandler: @escaping () -> Void) {
    completionHandlers.append(completionHandler)
}

@discardableResult

By default the compiler raises a warning when a operate returns with one thing, however that returned worth isn’t used. You possibly can suppress the warning by marking the return worth discardable with this Swift language attribute. ⚠️

@discardableResult func logAdd(_ a: Int, _ b: Int) -> Int {
    let c = a + b
    print(c)
    return c
}
logAdd(1, 2)

@autoclosure

This attribute can magically flip a operate with a closure parameter that has no arguments, however a return kind, right into a operate with a parameter kind of that authentic closure return kind, so you may name it far more straightforward. 🤓

func log(_ closure: @autoclosure () -> String) {
    print(closure())
}

log("b") 

@testable

In case you mark an imported module with the @testable attribute all the interior access-level entities shall be seen (out there) for testing functions. 👍

@testable import CoreKit

@objc

This attribute tells the compiler {that a} declaration is on the market to make use of in Goal-C code. Optionally you may present a single identifier that’ll be the identify of the Goal-C illustration of the unique entity. 🦖

@objc(LegacyClass)
class ExampleClass: NSObject {

    @objc non-public var retailer: Bool = false

    @objc var enabled: Bool {
        @objc(isEnabled) get {
            return self.retailer
        }
        @objc(setEnabled:) set {
            self.retailer = newValue
        }
    }

    @objc(setLegacyEnabled:)
    func set(enabled: Bool) {
        self.enabled = enabled
    }
}

@nonobjc

Use this attribute to supress an implicit objc attribute. The @nonobjc attribute tells the compiler to make the declaration unavailable in Goal-C code, regardless that it’s attainable to characterize it in Goal-C. 😎

@nonobjc static let check = "check"

@conference

This attribute point out operate calling conventions. It may well have one parameter which signifies Swift operate reference (swift), Goal-C appropriate block reference (block) or C operate reference (c).

func a(a: Int) -> Int {
    return a
}
let exampleSwift: @conference(swift) (Int) -> Int = a
exampleSwift(10)

Personal attributes

Personal Swift language attributes ought to solely be utilized by the creators of the language, or hardcore builders. They often present further (compiler) performance that’s nonetheless work in progress, so please be very cautious… 😳

Please don’t use non-public attributes in manufacturing code, except you actually know what you’re doing!!! 😅

@_exported

If you wish to import an exterior module in your complete module you should utilize the @_exported key phrase earlier than your import. From now the imported module shall be out there in every single place. Keep in mind PCH information? 🙃

@_exported import UIKit

@inline

With the @inline attribute you explicitly inform the compiler the operate inlining conduct. For instance if a operate is sufficiently small or it is solely getting referred to as just a few occasions the compiler is possibly going to inline it, except you disallow it explicitly.

@inline(by no means) func a() -> Int {
    return 1
}

@inline(__always) func b() -> Int {
    return 2
}

@_inlineable public func c() {
    print("c")
}
c()

@inlinable is the longer term (@_inlineable) by Marcin Krzyzanowskim 👏

@results

The @results attribute describes how a operate impacts “the state of the world”. Extra virtually how the optimizer can modify this system primarily based on data that’s offered by the attribute. You will discover the corresponding docs right here.

@results(readonly) func foo() {  }

@_transparent

Principally you may drive inlining with the @_transparent attribute, however please learn the unofficial documentation for more information.

@_transparent
func instance() {
    print("instance")
}

@_specialize

With the @_specialize Swift attribute you can provide hints for the compiler by itemizing concrete varieties for the generic signature. Extra detailed docs are right here.

struct S<T> {
  var x: T
  @_specialize(the place T == Int, U == Float)
  mutating func exchangeSecond<U>(_ u: U, _ t: T) -> (U, T) {
    x = t
    return (u, x)
  }
}

@_semantics

The Swift optimizer can detect code in the usual library whether it is marked with particular attributes @_semantics, that identifies the features. You possibly can examine semantics right here and right here, or inside this concurrency proposal.

@_semantics("array.depend")
func getCount() -> Int {
    return _buffer.depend
}

@silgenname

This attribute specifies the identify {that a} declaration can have at hyperlink time. You possibly can examine it contained in the Commonplace Librery Programmers Handbook.

@_silgen_name("_destroyTLS")
inner func _destroyTLS(_ ptr: UnsafeMutableRawPointer?) {
  
}

@_cdecl

Swift compiler comes with a built-in libFuzzer integration, which you should utilize with the assistance of the @_cdecl annotation. You possibly can be taught extra about libFuzzer right here.

@_cdecl("LLVMFuzzerTestOneInput") 
public func fuzzMe(Knowledge: UnsafePointer<CChar>, Dimension: CInt) -> CInt{
    
  }
}

Unavailable, undocumented, unknown

As you may see that is already fairly a listing, however there may be much more. Contained in the official Swift repository you will discover the attr checks. In case you want extra data in regards to the remaining Swift annotations you may go instantly there and test the supply code feedback. In case you might assist me writing in regards to the leftovers, please drop me just a few strains, I might actually recognize any assist. 😉👍

• @requiresstoredproperty_inits
• @warnunqualifiedaccess
• @fixedlayout
• @_versioned
• @showin_interface
• @_alignment
• @objcnonlazy_realization
• @_frozen
• @_optimize(none|pace|measurement)
• @_weakLinked
• @consuming
• @_restatedObjCConformance
• @_staticInitializeObjCMetadata
• @setterAccess
• @rawdoccomment
• @objc_bridged
• @noescape -> eliminated, see @escaping
• @noreturn -> eliminated, see By no means kind
• @downgradeexhaustivity_check -> no impact on change case anymore?
• @_implements(…) – @implements(Equatable, ==(:_:))
• @swiftnativeobjcruntime_base(class)

The @_implements attribute, which treats a decl because the implementation for some named protocol requirement (however in any other case not-visible by that identify).

This attribute signifies a category that ought to be handled semantically as a local Swift root class, however which inherits a selected Goal-C class at runtime. For many lessons that is the runtime’s “SwiftObject” root class. The compiler doesn’t must know in regards to the class; it is the construct system’s accountability to hyperlink towards the ObjC code that implements the basis class, and the ObjC implementation’s accountability to make sure situations start with a Swift-refcounting-compatible object header and override all the required NSObject refcounting strategies.

This enables us to subclass an Goal-C class and use the quick Swift reminiscence allocator. If you wish to add some notes about these attributes, please contact me.