Added Pacore

Assets/Pacore/Runtime/ClassAttributeCache.cs

@@ -0,0 +1,57 @@
+using System.Collections.ObjectModel;
+using System.Collections.Generic;
+using System.Linq;
+using System;
+using UnityEngine;
+
+namespace PashaBibko.Pacore
+{
+    public static class ClassAttributeCache
+    {
+        private static Dictionary<Type, List<Type>> AttributeCache { get; set; }
+
+        public static ReadOnlyCollection<Type> GetAttributesOf<T>()
+        {
+            return AttributeCache.TryGetValue(typeof(T), out List<Type> classes)
+                ? classes.AsReadOnly()
+                : throw new ArgumentException($"Attribute [{nameof(T)}] is not used by any classes");
+        }
+
+        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.AfterAssembliesLoaded)]
+        private static void ScanAllAssemblies()
+        {
+            /* Fetches all the class types in all loaded assemblies */
+            Type[] classes = AppDomain.CurrentDomain.GetAssemblies() // Assembly[]
+                .SelectMany(assembly => assembly.GetTypes()) // IEnumerable<Type>
+                .Where(type => type.IsClass && !type.IsAbstract) // IEnumerable<Type>
+                .ToArray();
+
+            /* Allocates space for the cache */
+            AttributeCache = classes // Type[]
+                .Where(type => typeof(Attribute).IsAssignableFrom(type)) // IEnumerable<Type>
+                .ToDictionary
+                (
+                    keySelector: t => t,
+                    elementSelector: _ => new List<Type>()
+                ); // Dictionary<Type, List<Type>>
+
+            /* Finds which attributes are attached to what classes */
+            HashSet<Type> seen = new();
+            foreach (Type current in classes)
+            {
+                /* Tracks the seen attributes */
+                seen.Clear();
+                foreach (object attr in current.GetCustomAttributes(inherit: true))
+                {
+                    seen.Add(attr.GetType());
+                }
+
+                /* Adds the class type to each attribute in the dictionary */
+                foreach (Type type in seen)
+                {
+                    AttributeCache[type].Add(current);
+                }
+            }
+        }
+    }
+}