[Feature] Dependencies (#3)

This PR contains the work done to provide a simple dependency injection feature whenever required.

To provide further details about this work:
- [x] renamed the `Coordinator` target in the `Package` file as `Coordination`;
- [x] declared the `Dependencies` target in the `Package` file;
- [x] defined the `DependencyKey` public protocol;
- [x] implemented the `DependencyService` public service;
- [x] implemented the `Dependency` public property wrapper;

Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Reviewed-on: #3

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
+    }
+
+}

Sources/Dependencies/Protocols/DependencyKey.swift

@@ -0,0 +1,22 @@
+//
+//  DependencyKey.swift
+//  Dependencies
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+/// This protocol defines a key to use in the dependency service.
+public protocol DependencyKey {
+    
+    // MARK: Associated types
+    
+    /// The associated type representing the type of the dependency key's value.
+    associatedtype Value
+    
+    // MARK: Properties
+    
+    /// The default value for the dependency key.
+    static var currentValue: Value { get set }
+    
+}

Sources/Dependencies/Services/DependencyService.swift

@@ -0,0 +1,28 @@
+//
+//  DependencyService.swift
+//  Dependencies
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+/// This service provide write/read access to the injected dependencies.
+public struct DependencyService {
+    
+    // MARK: Properties
+    
+    private static var current = DependencyService()
+    
+    // MARK: Subscripts
+
+    public static subscript<DK: DependencyKey>(key: DK.Type) -> DK.Value {
+        get { key.currentValue }
+        set { key.currentValue = newValue }
+    }
+    
+    public static subscript<D>(_ keyPath: WritableKeyPath<DependencyService, D>) -> D {
+        get { current[keyPath: keyPath] }
+        set { current[keyPath: keyPath] = newValue }
+    }
+
+}