feat: init accessor

Author: sator-imaging

Runtime/IsExternalInit.cs

@@ -0,0 +1,14 @@
+#if false == UNITY_2022_1_OR_NEWER
+
+// NOTE: to use record & init accessor in Unity 2021
+//       https://stackoverflow.com/questions/62648189/testing-c-sharp-9-0-in-vs2019-cs0518-isexternalinit-is-not-defined-or-imported
+
+namespace System.Runtime.CompilerServices
+{
+    [ComponentModel.EditorBrowsable(ComponentModel.EditorBrowsableState.Never)]
+    /*internal*/ class IsExternalInit
+    {
+    }
+}
+
+#endif

Runtime/IsExternalInit.cs.meta

@@ -3,12 +3,11 @@
 
 namespace SatorImaging.UnitySourceGenerator
 {
-    // OPTIMIZE: Be ref struct
-    public class USGContext
+    public sealed class USGContext
     {
-        public Type TargetClass;
-        public string AssetPath;
-        public string OutputPath;
+        public Type TargetClass { get; init; }
+        public string AssetPath { get; init; }
+        public string OutputPath { get; set; }
 
     }
 }