Every thing 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

If you happen to 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 via 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 immediately 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 can 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 just draw inside your view can be rendered into the IB canvas.

@IBDesignable class MyCustomView: UIView {  }

@UIApplicationMain, @NSApplicationMain

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

@accessible

With the @accessible attribute you’ll be able to mark varieties accessible, deprecated, unavailable, and many others. for particular platforms. I am not going into the small print there are some nice posts about tips on how to use the attribute with availability checkings in Swift.

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

@NSCopying

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

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

@NSManaged

If you’re utilizing Core Knowledge entities (normally NSManagedObject subclasses), you’ll be able to 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 accessible 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 could 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 perform returns with one thing, however that returned worth is rarely 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 perform with a closure parameter that has no arguments, however a return sort, right into a perform with a parameter sort of that unique closure return sort, so you’ll be able to name it rather more simple. 🤓

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

log("b") 

@testable

If you happen to mark an imported module with the @testable attribute all the inner access-level entities can be seen (accessible) for testing functions. 👍

@testable import CoreKit

@objc

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

@objc(LegacyClass)
class ExampleClass: NSObject {

    @objc personal 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, although it’s attainable to signify it in Goal-C. 😎

@nonobjc static let check = "check"

@conference

This attribute point out perform calling conventions. It could possibly have one parameter which signifies Swift perform reference (swift), Goal-C suitable block reference (block) or C perform 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 normally present further (compiler) performance that’s nonetheless work in progress, so please be very cautious… 😳

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

@_exported

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

@_exported import UIKit

@inline

With the @inline attribute you explicitly inform the compiler the perform inlining conduct. For instance if a perform is sufficiently small or it is solely getting known as a couple of occasions the compiler is perhaps 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 long run (@_inlineable) by Marcin Krzyzanowskim 👏

@results

The @results attribute describes how a perform 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’ll be able to pressure 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 may give 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 capabilities. 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 could have at hyperlink time. You possibly can examine it contained in the Customary Librery Programmers Handbook.

@_silgen_name("_destroyTLS")
inside 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 study extra about libFuzzer right here.

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

Unavailable, undocumented, unknown

As you’ll be able to see that is already fairly a listing, however there’s much more. Contained in the official Swift repository you could find the attr exams. If you happen to want extra information concerning the remaining Swift annotations you’ll be able to go immediately there and verify the supply code feedback. If you happen to might assist me writing concerning the leftovers, please drop me a couple of strains, I would 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 sort
• @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 needs 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 have to know concerning the class; it is the construct system’s duty to hyperlink in opposition to the ObjC code that implements the foundation class, and the ObjC implementation’s duty to make sure cases start with a Swift-refcounting-compatible object header and override all the required NSObject refcounting strategies.

This permits 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.