Base class for attributes

namespace Deliverystack.Core.Attributes
{
    using System;
    using System.Collections.Concurrent;
    using System.Collections.Generic;
    using System.Reflection;

    public abstract class AttributeBase : Attribute
    {
        // map the type of the attribute to a list of types that have that attribute.
        // static and cached to optimize performance.
        private static ConcurrentDictionary<Type, List<Type>> _types =
            new ConcurrentDictionary<Type, List<Type>>();

        public static Type[] GetTypesWithAttribute(Type attribute)
        {
            // Have assemblies already been scanned for this attribute.
            if (!_types.ContainsKey(attribute))
            {
                // no, create a new entry in the dictionary mapping
                // the attribute to the list of types that have that attribute.
                List<Type> result = new List<Type>();

                // for each assembly available
                foreach (Assembly assembly in AppDomain.CurrentDomain.GetAssemblies())
                {
                    try
                    {
                        // for each type in the assembly
                        foreach (Type type in assembly.GetTypes())
                        {
                            // if the type has the attribute
                            if (type.GetCustomAttributes(attribute, true).Length > 0)
                            {
                                // then add it to the list of types for the attribute
                                result.Add(type);
                            }
                        }
                    }
                    catch (Exception ex)
                    {
                        // ignore; unable to load; assembly may be obfuscated, etc.
                    }
                }

                // store a record mapping the attribute to the list of types with that attribute
                _types[attribute] = result;
            }

            // return the list of types with the attribute
            return _types[attribute].ToArray();
        }
    }
}