Overview

SwiftCopyableMacro is a very simple Swift macro library that auto-generates a copy() function for structs at compile time, which takes all the public properties of the struct as arguments in the function, enabling a runtime ability to elegantly duplicate an instance of the struct and setting new values for any or all these (even immutable) properties at the same time, similar to what Kotlin's data class offers.

The only effort required is to mark the structs with a custom @Copyable annotation and the structs are automatically injected with a copy() method inside. For example:

@Copyable // <= annotation is used here
struct User {
    let name: String
    let age: Int
}

automatically updates the struct at compile time (which happens instantly if editing the file inside of Xcode) as follows:

struct User {
    let name: String
    let age: Int

    // Notice the arguments for the function 👇
    func copy(name: String? = nil, age: Int? = nil) -> Self {
        .init(
            name: name ?? self.name
            age: age ?? self.age
        )
    }
}

This struct can now be used at a call site like so:

let ugo = User(name: "Ugo", age: 30)
print(ugo) // Ugo(name: "Ugo", age: 30)

let ugoAsJack = ugo.copy(name: "Jack") // <= .copy() is used here
print(ugoAsJack) // Ugo(name: "Jack", age: 30)

let ugoIsOlder = ugo.copy(age: 34) // <= .copy() is used here
print(ugoIsOlder) // Ugo(name: "Ugo", age: 34)
print(ugoAsJack) // Ugo(name: "Jack", age: 30)

let jackIsYounger = ugoAsJack.copy(age: 25) // <= .copy() is used here
print(jackIsYounger) // Ugo(name: "Jack", age: 25)

Xcode will even offer autocomplete listing all the properties declared in the struct as parameters in this .copy(...) function.

Installation

This macro is available for installation via the Swift Package Manager (SPM) as follows:

Xcode

1. In Xcode, select the menu: File → Add Package Dependencies… to launch the SPM dialog;
2. in the "Search or Enter Package URL" text field, enter the package URL: https://github.com/ugommirikwe/SwiftCopyableMacro;
3. in "Dependency Rule" select "Branch";
4. in the "Branch" text field enter the value "main"
5. select the project to add the

package.swift

For projects that use a package.swift file to manage their SPM dependencies, you can add it to your package.swift file like so:

dependencies: [
    .package(url: "https://github.com/ugommirikwe/SwiftCopyableMacro", .branch("main"))
]

And then add the product to all targets that use CopyableMacro:

...
targets: [
    .target(
        name: "<NameOfYourTarget>", 
        dependencies: ["CopyableMacro"],
    )
]

Import & Usage

The overview section above already describes how to use the macro: prepend your struct name with the annotation @Copyable and that's all. Xcode 15+ should automatically add the import at the top of the file for you. Otherwise, go ahead and add it as follows to clear any errors in your file:

import CopyableMacro

Pre-Release

Please note that this code is still in pre-release stage and should be carefully evaluated before using in your production code.

Feedback and Issues

Feel free to submit any issues or suggestions. Pull requests are also welcomed.

License

SwiftCopyableMacro is available under the MIT license. See the LICENSE file for more info.