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Swift '@...' Quiz: Where Do They Come From?

2024/12/20に公開

When writing code in Swift, you may sometimes use expressions starting with the @ symbol, such as @〜〜〜. Do you know exactly what that @〜〜〜 is and where it came from?

This article is for Day 20 of the Swift Advent Calendar 2024.

Swift's `@〜〜〜`

In Swift, the @〜〜〜 syntax is used to indicate the following five things:

"Attributes" in the Swift language
- Types of attributes
  - Declaration attributes
  - Type attributes
  - Switch case attributes
"Property wrappers," a feature of the Swift language
"Result builders," a feature of the Swift language
"Global actors," a feature of the Swift language
"Attached macros," a feature of the Swift language

For example, when developing iOS applications using Swift, you might use things like @main, @State, @ViewBuilder, @MainActor, and @Model. All of these can be classified into one of the five categories above. Furthermore, if it is a "property wrapper," "result builder," "global actor," or "attached macro," it is defined within some framework.

Examples

Q0-1. What is @main and where does it come from?

Answer for Q0-1. @main
`@main` is an "attribute (declaration attribute)" defined in the "Swift language itself."

Q0-2. What is @State and where does it come from?

Answer for Q0-2. @State
`@State` is a "property wrapper" defined in the "SwiftUI framework."

Q0-3. What is @ViewBuilder and where does it come from?

Answer for Q0-3. @ViewBuilder
`@ViewBuilder` is a "result builder" defined in the "SwiftUI framework."

Q0-4. What is @MainActor and where does it come from?

Answer for Q0-4. @MainActor
`@MainActor` is a "global actor" defined in the "Swift language (Swift Standard Library)."

Q0-5. What is @Model and where does it come from?

Answer for Q0-5. @Model
`@Model` is an "attached macro" defined in the "SwiftData framework."

Quiz - Beginner

Q1-1. What is @EnvironmentObject and where does it come from?

Answer for Q1-1. @EnvironmentObject

@EnvironmentObject is a "property wrapper" defined in the "SwiftUI framework."

Q1-2. What is @Binding and where does it come from?

Answer for Q1-2. @Binding

@Binding is a "property wrapper" defined in the "SwiftUI framework."

Q1-3. What is @Published and where does it come from?

Answer for Q1-3. @Published

@Published is a "property wrapper" defined in the "Combine framework."
(However, in environments where the "Combine framework" can be used, there is also a typealias definition in the "Foundation framework.")

Q1-4. What is @Observable and where does it come from?

Answer for Q1-4. @Observable

@Observable is an "attached macro" defined in the "Swift language (Observation framework)."

Q1-5. What is @SceneBuilder and where does it come from?

Answer for Q1-5. @SceneBuilder

@SceneBuilder is a "result builder" defined in the "SwiftUI framework."

Q1-6. What is @AppStorage and where does it come from?

Answer for Q1-6. @AppStorage

@AppStorage is a "property wrapper" defined in the "SwiftUI framework."

Q1-7. What is @Test and where does it come from?

Answer for Q1-7. @Test

@Test is an "attached macro" defined in the "Swift language (Testing framework)."

Q1-8. What is @testable and where does it come from?

Answer for Q1-8. @testable

@testable is an "attribute (declaration attribute)" defined in the "Swift language itself."

Q1-9. What is @escaping and where does it come from?

Answer for Q1-9. @escaping

@escaping is an "attribute (type attribute)" defined in the "Swift language itself."

Q1-10. What is @UIApplicationMain and where does it come from?

Answer for Q1-10. @UIApplicationMain

@UIApplicationMain is an "attribute (declaration attribute)" defined in the "Swift language itself."

Quiz - Intermediate

Q2-1. What is @Bindable and where does it come from?

Answer for Q2-1. @Bindable

@Bindable is a "property wrapper" defined in the "SwiftUI framework."

Q2-2. What is @Environment and where does it come from?

Answer for Q2-2. @Environment

@Environment is a "property wrapper" defined in the "SwiftUI framework."

Q2-3. What is @Previewable and where does it come from?

Answer for Q2-3. @Previewable

@Previewable is an "attached macro" defined in the "SwiftUI framework."

Q2-4. What is @Query and where does it come from?

Answer for Q2-4. @Query

@Query is an "attached macro" defined in the "SwiftData framework."

Q2-5. What is @MapContentBuilder and where does it come from?

Answer for Q2-5. @MapContentBuilder

@MapContentBuilder is a "result builder" defined in the "MapKit framework and SwiftUI framework."

Q2-6. What is @UIApplicationDelegateAdaptor and where does it come from?

Answer for Q2-6. @UIApplicationDelegateAdaptor

@UIApplicationDelegateAdaptor is a "property wrapper" defined in the "SwiftUI framework."

Q2-7. What is @Suite and where does it come from?

Answer for Q2-7. @Suite

@Suite is an "attached macro" defined in the "Swift language (Testing framework)."

Q2-8. What is @unchecked and where does it come from?

Answer for Q2-8. @unchecked

@unchecked is an "attribute (declaration attribute)" defined in the "Swift language itself."

Q2-9. What is @Sendable and where does it come from?

Answer for Q2-9. @Sendable

@Sendable is an "attribute (type attribute)" defined in the "Swift language itself."

Q2-10. What is @preconcurrency and where does it come from?

Answer for Q2-10. @preconcurrency

@preconcurrency is an "attribute (declaration attribute)" defined in the "Swift language itself."

Quiz - Advanced

Q3-1. What is @Entry and where does it come from?

Answer for Q3-1. @Entry

@Entry is an "attached macro" defined in the "SwiftUI framework."

Q3-2. What is @unknown and where does it come from?

Answer for Q3-2. @unknown

@unknown is an "attribute (switch case attribute)" defined in the "Swift language itself."

Q3-3. What is @Tag and where does it come from?

Answer for Q3-3. @Tag

@Tag is an "attached macro" defined in the "Swift language (Testing framework)."

Q3-4. What is @ModelActor and where does it come from?

Answer for Q3-4. @ModelActor

@ModelActor is an "attached macro" defined in the "SwiftData framework."

Q3-5. What is @ViewLoading and where does it come from?

Answer for Q3-5. @ViewLoading

@ViewLoading is a "property wrapper" defined in the "AppKit framework" or "UIKit framework."

Q3-6. What is @propertyWrapper and where does it come from?

Answer for Q3-6. @propertyWrapper

@propertyWrapper is an "attribute (declaration attribute)" defined in the "Swift language itself."

Q3-7. What is @CodableConfiguration and where does it come from?

Answer for Q3-7. @CodableConfiguration

@CodableConfiguration is a "property wrapper" defined in the "Swift language (Foundation)."

Q3-8. What is @resultBuilder and where does it come from?

Answer for Q3-8. @resultBuilder

@resultBuilder is an "attribute (declaration attribute)" defined in the "Swift language itself."

Q3-9. What is @TransferRepresentationBuilder and where does it come from?

Answer for Q3-9. @TransferRepresentationBuilder

@TransferRepresentationBuilder is a "result builder" defined in the "Core Transferable framework."

Q3-10. What is @TaskLocal and where does it come from?

Answer for Q3-10. @TaskLocal

@TaskLocal is defined in the "Swift language"; it was a "property wrapper" before Swift 6.0, and has been an "attached macro" since Swift 6.0.

Answer List / Reference Links

Examples

0-1. `@main`

Syntax	From
Attribute (declaration attribute)	Swift Language itself

0-2. `@State`

Syntax	From
Property wrapper	SwiftUI framework

0-3. `@ViewBuilder`

Syntax	From
Result builder	SwiftUI framework

0-4. `@MainActor`

Syntax	From
Global actor	Swift language (Swift Standard Library)

0-5. `@Model`

Syntax	From
Attached macro	SwiftData framework

Beginner

1-1. @EnvironmentObject

Syntax	From
Property wrapper	SwiftUI framework

1-2. @Binding

Syntax	From
Property wrapper	SwiftUI framework

1-3. @Published

Syntax	From
Property wrapper	Combine framework
(typealias definition for the above)	(Foundation framework)

1-4. @Observable

Syntax	From
Attached macro	Swift language (Observation framework)

1-5. @SceneBuilder

Syntax	From
Result builder	SwiftUI framework

1-6. @AppStorage

Syntax	From
Property wrapper	SwiftUI framework

1-7. @Test

Syntax	From
Attached macro	Swift language (Testing framework)

1-8. @testable

Syntax	From
Attribute (declaration attribute)	Swift language itself

1-9. @escaping

Syntax	From
Attribute (type attribute)	Swift language itself

1-10. @UIApplicationMain

Syntax	From
Attribute (declaration attribute)	Swift language itself

Intermediate

2-1. `@Bindable`

Syntax	From
Property wrapper	SwiftUI framework

2-2. `@Environment`

Syntax	From
Property wrapper	SwiftUI framework

2-3. `@Previewable`

Syntax	From
Attached macro	SwiftUI framework

2-4. `@Query`

Syntax	From
Attached macro	SwiftData framework

2-5. `@MapContentBuilder`

Syntax	From
Result builder	MapKit framework and SwiftUI framework

2-6. `@UIApplicationDelegateAdaptor`

Syntax	From
Property wrapper	SwiftUI framework

2-7. `@Suite`

Syntax	From
Attached macro	Swift language (Testing framework)

2-8. `@unchecked`

Syntax	From
Attribute (declaration attribute)	Swift language itself

2-9. `@Sendable`

Syntax	From
Attribute (type attribute)	Swift language itself

2-10. `@preconcurrency`

Syntax	From
Attribute (declaration attribute)	Swift language itself

Advanced

3-1. `@Entry`

Syntax	From
Attached macro	SwiftUI framework

3-2. `@unknown`

Syntax	From
Attribute (switch case attribute)	Swift language itself

3-3. `@Tag`

Syntax	From
Attached macro	Swift language (Testing framework)

3-4. `@ModelActor`

Syntax	From
Attached macro	SwiftData framework

3-5. `@ViewLoading`

Syntax	From
Property wrapper	AppKit framework
Property wrapper	UIKit framework

3-6. `@propertyWrapper`

Syntax	From
Attribute (declaration attribute)	Swift language itself

3-7. `@CodableConfiguration`

Syntax	From
Property wrapper	Swift language (Foundation)

3-8. `@resultBuilder`

Syntax	From
Attribute (declaration attribute)	Swift language itself

3-9. `@TransferRepresentationBuilder`

Syntax	From
Result builder	Core Transferable framework

3-10. `@TaskLocal`

Syntax	From
Before Swift 6.0: Property wrapper	Swift language
From Swift 6.0: Attached macro	Swift language

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iTranslated by AI

Swift's @〜〜〜

Examples

Quiz - Beginner

Quiz - Intermediate

Quiz - Advanced

Answer List / Reference Links

Examples

0-1. @main

0-2. @State

0-3. @ViewBuilder

0-4. @MainActor

0-5. @Model

Beginner

1-1. @EnvironmentObject

1-2. @Binding

1-3. @Published

1-4. @Observable

1-5. @SceneBuilder

1-6. @AppStorage

1-7. @Test

1-8. @testable

1-9. @escaping

1-10. @UIApplicationMain

Intermediate

2-1. @Bindable

2-2. @Environment

2-3. @Previewable

2-4. @Query

2-5. @MapContentBuilder

2-6. @UIApplicationDelegateAdaptor

2-7. @Suite

2-8. @unchecked

2-9. @Sendable

2-10. @preconcurrency

Advanced

3-1. @Entry

3-2. @unknown

3-3. @Tag

3-4. @ModelActor

3-5. @ViewLoading

3-6. @propertyWrapper

3-7. @CodableConfiguration

3-8. @resultBuilder

3-9. @TransferRepresentationBuilder

3-10. @TaskLocal

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Discussion

Swift's `@〜〜〜`

0-1. `@main`

0-2. `@State`

0-3. `@ViewBuilder`

0-4. `@MainActor`

0-5. `@Model`

2-1. `@Bindable`

2-2. `@Environment`

2-3. `@Previewable`

2-4. `@Query`

2-5. `@MapContentBuilder`

2-6. `@UIApplicationDelegateAdaptor`

2-7. `@Suite`

2-8. `@unchecked`

2-9. `@Sendable`

2-10. `@preconcurrency`

3-1. `@Entry`

3-2. `@unknown`

3-3. `@Tag`

3-4. `@ModelActor`

3-5. `@ViewLoading`

3-6. `@propertyWrapper`

3-7. `@CodableConfiguration`

3-8. `@resultBuilder`

3-9. `@TransferRepresentationBuilder`

3-10. `@TaskLocal`