Another Implementation for the Service Locator pattern is added.

Assets/Patterns/15. Service Locator (Another Implementation)/GameController.cs

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+namespace ServiceLocatorPattern
+{
+    using UnityEngine;
+
+    public class GameController : MonoBehaviour
+    {
+        private void Start()
+        {
+            var firstService = ServiceLocator.Resolve<FirstService>();
+            var secondService = ServiceLocator.Resolve<SecondService>();
+            var thirdService = ServiceLocator.Resolve<ThirdService>();
+
+            firstService?.SayHi();
+            secondService?.SimpleMethod();
+            thirdService?.Foo();
+        }
+    }
+}

Assets/Patterns/15. Service Locator (Another Implementation)/ServiceLocator.cs

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+using System.Collections.Generic;
+using System.Linq;
+
+namespace ServiceLocatorPattern
+{
+    public static class ServiceLocator
+    {
+        private static readonly HashSet<object> _registeredObjects;
+
+        static ServiceLocator()
+        {
+            _registeredObjects = new HashSet<object>();
+        }
+
+        public static void Register<T>(T obj) where T : class
+        {
+            _registeredObjects.Add(obj);
+        }
+
+        public static void Unregister<T>(T obj) where T : class
+        {
+            _registeredObjects.Remove(obj);
+        }
+
+        public static T Resolve<T>() where T : class
+        {
+            var obj = _registeredObjects.SingleOrDefault(x => x is T);
+            if (obj != null)
+                return obj as T;
+
+            return null;
+        }
+    }
+}