initial copyable

Author: matthew-shin-hs

.gitignore

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+.DS_Store
+
 # Xcode
 #
 # gitignore contributors: remember to update Global/Xcode.gitignore, Objective-C.gitignore & Swift.gitignore

.swiftpm/xcode/package.xcworkspace/contents.xcworkspacedata

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+{
+  "originHash" : "8d9aa6d1ffb40aaa702c8b3825eb1a9dd7101dbed3d6781ef954028fa38aed6f",
+  "pins" : [
+    {
+      "identity" : "swift-syntax",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/apple/swift-syntax.git",
+      "state" : {
+        "revision" : "2bc86522d115234d1f588efe2bcb4ce4be8f8b82",
+        "version" : "510.0.3"
+      }
+    }
+  ],
+  "version" : 3
+}

Package.resolved

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+//Copyright © 2024 Hootsuite Media Inc. All rights reserved.
+
+// swift-tools-version: 6.0
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+import CompilerPluginSupport
+
+let package = Package(
+    name: "Macros",
+    platforms: [.macOS(.v10_15), .iOS(.v13), .tvOS(.v13), .watchOS(.v6), .macCatalyst(.v13)],
+    products: [
+        // Products define the executables and libraries a package produces, making them visible to other packages.
+        .library(
+            name: "Macros",
+            targets: ["Macros"]
+        ),
+        .executable(
+            name: "MacrosClient",
+            targets: ["MacrosClient"]
+        ),
+    ],
+    dependencies: [
+        .package(url: "https://github.com/apple/swift-syntax.git", "509.0.0"..<"600.0.0"),
+    ],
+    targets: [
+        // Targets are the basic building blocks of a package, defining a module or a test suite.
+        // Targets can depend on other targets in this package and products from dependencies.
+        // Macro implementation that performs the source transformation of a macro.
+        .macro(
+            name: "MacrosImplementation",
+            dependencies: [
+                .product(name: "SwiftSyntaxMacros", package: "swift-syntax"),
+                .product(name: "SwiftCompilerPlugin", package: "swift-syntax")
+            ]
+        ),
+
+        // Library that exposes a macro as part of its API, which is used in client programs.
+        .target(name: "Macros", dependencies: ["MacrosImplementation"]),
+
+        // A client of the library, which is able to use the macro in its own code.
+        .executableTarget(name: "MacrosClient", dependencies: ["Macros"]),
+
+        // A test target used to develop the macro implementation.
+        .testTarget(
+            name: "MacrosTests",
+            dependencies: [
+                "MacrosImplementation",
+                .product(name: "SwiftSyntaxMacrosTestSupport", package: "swift-syntax"),
+            ]
+        ),
+    ]
+)

Package.swift

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 # copyable-macro
 Copyable is a Swift Macro used to bring Kotlin's `copy` functionality to Swift.
+ 
+
+## Functionality
+Creates a new instance of the struct with all properties copied from the original, allowing selective modification of specific properties while keeping others unchanged 
+
+## Swift Package Manager
+In `Package.swift`:
+
+```swift
+dependencies: [
+    .package(url: "https://github.com/hootsuite/copyable-macro.git", from: "1.0.0")
+]
+```
+
+## Usage
+
+1.
+
+```swift
+import Copyable
+
+@Copyable
+struct Student {
+    let name: String
+    let grade: Int
+}
+
+let student1 = Student(name: "Matthew", grade: 100)
+
+print("name: \(student1.name) grade: \(student1.grade))
+
+// should print: "name: Matthew grade: 100" 
+
+let student 2 = student1.copy { student in  
+    student.name = "Henry"
+}
+
+print("name: \(student2.name) grade: \(student2.grade))
+
+// should print: "name: Henry grade: 100"
+```

README.md

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+//Copyright © 2024 Hootsuite Media Inc. All rights reserved.
+
+/// A macro that creates an extension on a struct to give a kotlin-like copy functionality
+/// source code from: https://shopify.engineering/kotlin-style-copy-function-swift-structs
+/// Used to make a copy of the struct while updating values passed in as parameters into a closure that receives the builder as the sole argument, and allows you to set overrides for selected properties.
+@attached(extension, conformances: Equatable, names: arbitrary)
+public macro Copyable() = #externalMacro(module: "MacrosImplementation", type: "CopyableMacro")

Sources/Macros/Macros.swift

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+//Copyright © 2024 Hootsuite Media Inc. All rights reserved.
+
+import Copyable
+
+//MARK: @Copyable example
+
+@Copyable
+struct Student {
+    let name: String
+    let grade: Int
+    
+    // if default params are to be used, must create custom init methods like below
+    init(
+        name: String = "1",
+        grade: Int = 2
+    ) {
+        self.name = name
+        self.grade = grade
+    }
+}
+
+let student1 = Student(name: "Matt", grade: 100)
+let student2 = student1.copy { $0.name = "Borys" }
+
+print("\(student1.name) has a grade of \(student1.grade)")
+print("\(student2.name) has a grade of \(student2.grade)")
+
+// Copyable can also be used with vars
+
+@Copyable
+struct Hotel {
+    var name: String
+    var foundingYear: Int
+}
+
+let hotel = Hotel(name: "Hootsuite Inn", foundingYear: 2021)
+let newHotel = hotel.copy { $0.name = "Hootsuite Tower" }
+
+print("\(hotel.name) was founded in \(hotel.foundingYear)")
+print("\(newHotel.name) was founded in \(newHotel.foundingYear)")
+