First commit

Runtime/Helpers/ReadOnlyCollectionExtension.cs

@@ -0,0 +1,21 @@
+using System;
+using System.Collections.ObjectModel;
+
+namespace Misaki.GraphView
+{
+    public static class ReadOnlyCollectionExtension
+    {
+        public static int FindIndex<T>(this ReadOnlyCollection<T> collection, Predicate<T> match)
+        {
+            for (var i = 0; i < collection.Count; i++)
+            {
+                if (match(collection[i]))
+                {
+                    return i;
+                }
+            }
+
+            return -1;
+        }
+    }
+}