Implemented the Dependency property wrapper.

Sources/Dependencies/Property Wrappers/Dependency.swift

@@ -0,0 +1,31 @@
+//
+//  Dependency.swift
+//  Dependencies
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+/// This property wrapper provides a direct connection to the `DependencyService` service.
+@propertyWrapper
+public struct Dependency<D> {
+    
+    // MARK: Properties
+    
+    private let keyPath: WritableKeyPath<DependencyService, D>
+    
+    /// This property allows direct read/write access to a defined dependency attached to a selected key path.
+    public var wrappedValue: D {
+        get { DependencyService[keyPath] }
+        set { DependencyService[keyPath] = newValue }
+    }
+    
+    // MARK: Initialisers
+    
+    /// Initialise the property wrapper by setting a key path to a defined dependency.
+    /// - Parameter keyPath: A key path to a defined dependency in the `DependencyService` service.
+    public init(_ keyPath: WritableKeyPath<DependencyService, D>) {
+        self.keyPath = keyPath
+    }
+
+}

Tests/Dependencies/Property Wrappers/DependencyTests.swift

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+//
+//  DependencyTests.swift
+//  DependenciesTests
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import Dependencies
+import XCTest
+
+final class DependencyTests: XCTestCase {
+    
+    // MARK: Properties
+    
+    private var subject: TestSubject!
+    
+    // MARK: Setup
+    
+    override func setUp() {
+        DependencyService[\.testService] = SomeService()
+    }
+    
+    // MARK: Tests
+
+    func test_readTestService() {
+        // GIVEN
+        subject = .init()
+        
+        // WHEN
+        let service = subject.testService
+        
+        // THEN
+        XCTAssertNotNil(service)
+        XCTAssert(service is SomeService)
+    }
+    
+    func test_writeDependencyKey() async throws {
+        // GIVEN
+        subject = .init()
+        
+        subject.testService = SomeOtherService()
+        
+        // WHEN
+        let service = DependencyService[\.testService]
+        
+        // THEN
+        XCTAssertNotNil(service)
+        XCTAssert(service is SomeOtherService)
+    }
+    
+    func test_writeDependencyKeyTwice() async throws {
+        // GIVEN
+        subject = .init()
+        
+        subject.testService = SomeOtherService()
+        subject.testService = SomeService()
+        
+        // WHEN
+        let service = DependencyService[\.testService]
+        
+        // THEN
+        XCTAssertNotNil(service)
+        XCTAssert(service is SomeService)
+    }
+
+}
+
+// MARK: - TestSubject
+
+private struct TestSubject {
+    @Dependency(\.testService) var testService
+}