All the pieces about private and non-private Swift attributes

Have you ever ever heard about Swift language attributes? On this article I am making an attempt to collect all of the @ annotations and their meanings.

Public attributes

Public Swift language attributes are marked with the @ image, they’re (roughly) effectively documented and prepared to be used. Right here is the entire 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 along with your visuals by way of the offered “outlet” mechanism.

@IBOutlet weak var textLabel: UILabel!

@IBAction

Equally, @IBAction is an attribute that makes potential connecting actions despatched from Interface Builder. So the marked technique 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 habits as @IBInspectable, however the property might be uncovered for the SpriteKit editor UI as a substitute 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 might be rendered into the IB canvas.

@IBDesignable class MyCustomView: UIView {  }

@UIApplicationMain, @NSApplicationMain

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

@obtainable

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

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

@NSCopying

You’ll be able to mark a property with this attribute to make a duplicate of it as a substitute of the worth of the property iself. Clearly this may be actually useful while you copy reference sorts.

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

@NSManaged

If you’re utilizing Core Information entities (normally NSManagedObject subclasses), you may mark saved variables or occasion strategies as @NSManaged to point that the Core Information framework will dynamically present the implementation at runtime.

class Particular person: NSManagedObject {
    @NSManaged var identify: NSString
}

@objcMembers

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

@objcMembers class Particular person {
    var firstName: String?
    var lastName: String?
}

@escaping

You’ll be able to mark closure parameters as @escaping, if you wish to point out that the worth may 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’ll be able to 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 sort, right into a operate with a parameter sort of that authentic closure return sort, so you may name it rather 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 might be seen (obtainable) for testing functions. 👍

@testable import CoreKit

@objc

This attribute tells the compiler {that a} declaration is obtainable 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, although it’s potential to characterize it in Goal-C. 😎

@nonobjc static let take a look at = "take a look at"

@conference

This attribute point out operate calling conventions. It may have one parameter which signifies Swift operate reference (swift), Goal-C suitable 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 normally present additional (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 entire module you need to use the @_exported key phrase earlier than your import. From now the imported module might be obtainable all over the place. Keep in mind PCH recordsdata? 🙃

@_exported import UIKit

@inline

With the @inline attribute you explicitly inform the compiler the operate inlining habits. For instance if a operate is sufficiently small or it is solely getting known 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 long run (@_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 based mostly on info that’s offered by the attribute.

You could find the corresponding docs right here.

@results(readonly) func foo() {  }

@_transparent

Mainly you may 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 sorts 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’ll be able to 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’ll be able to examine it contained in the Commonplace Librery Programmers Guide.

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

@_cdecl

Swift compiler comes with a built-in libFuzzer integration, which you need to use with the assistance of the @_cdecl annotation. You’ll be able to be taught extra about libFuzzer right here.

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

Unavailable, undocumented, unknown

As you may see that is already fairly a listing, however there’s much more. Contained in the official Swift repository you’ll find the attr assessments. In case you want extra information in regards to the remaining Swift annotations you may go immediately there and examine the supply code feedback. In case you might assist me writing in regards to the leftovers, please drop me just a few traces, I would actually respect any assist. 😉👍

• @requiresstoredproperty_inits
• @warnunqualifiedaccess
• @fixedlayout
• @_versioned
• @showin_interface
• @_alignment
• @objcnonlazy_realization
• @_frozen
• @_optimize(none|pace|dimension)
• @_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 must 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 duty to hyperlink towards the ObjC code that implements the foundation class, and the ObjC implementation’s duty to make sure situations start with a Swift-refcounting-compatible object header and override all the mandatory 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 on twitter.