Add SoftObjectReference for lazy references to assets and objects

Source/Engine/Scripting/SoftObjectReference.cs

@@ -0,0 +1,80 @@
+// Copyright (c) 2012-2021 Wojciech Figat. All rights reserved.
+
+using System;
+
+namespace FlaxEngine
+{
+    /// <summary>
+    /// The scripting object soft reference. Objects gets referenced on use (ID reference is resolving it).
+    /// </summary>
+    public struct SoftObjectReference : IComparable, IComparable<SoftObjectReference>
+    {
+        private Guid _id;
+        private Object _object;
+
+        /// <summary>
+        /// Gets or sets the object identifier.
+        /// </summary>
+        public Guid ID
+        {
+            get => _id;
+            set
+            {
+                if (_id == value)
+                    return;
+                _id = value;
+                _object = null;
+            }
+        }
+
+        /// <summary>
+        /// Gets the object reference.
+        /// </summary>
+        /// <typeparam name="T">The object type.</typeparam>
+        /// <returns>The resolved object or null.</returns>
+        public T Get<T>() where T : Object
+        {
+            if (!_object)
+                _object = Object.Find(ref _id, typeof(T));
+            return _object as T;
+        }
+
+        /// <summary>
+        /// Sets the object reference.
+        /// </summary>
+        /// <param name="obj">The object.</param>
+        public void Set(Object obj)
+        {
+            _object = obj;
+            _id = obj?.ID ?? Guid.Empty;
+        }
+
+        /// <inheritdoc />
+        public override string ToString()
+        {
+            if (_object)
+                return _object.ToString();
+            return _id.ToString();
+        }
+
+        /// <inheritdoc />
+        public override int GetHashCode()
+        {
+            return _id.GetHashCode();
+        }
+
+        /// <inheritdoc />
+        public int CompareTo(object obj)
+        {
+            if (obj is SoftObjectReference other)
+                return CompareTo(other);
+            return 0;
+        }
+
+        /// <inheritdoc />
+        public int CompareTo(SoftObjectReference other)
+        {
+            return _id.CompareTo(other._id);
+        }
+    }
+}