gistfile1.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Diagnostics;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;

namespace ConsoleApplication12 {
    class Program {
        static void Main(string[] args) {
            var sw = new Stopwatch();
            var iterations = 50000;
            // Warmup
            AttributeRetriever.GetAttribute<Model, string>(x => x.Name, typeof (PrivilegeAttribute), "Privilege");

            sw.Start();
            for(var i = 0; i < iterations; i++) {
                AttributeRetriever.GetAttribute<Model, string>(x => x.Name, typeof(PrivilegeAttribute), "Privilege");
            }
            sw.Stop();

            Console.WriteLine("Took {0} ms", sw.ElapsedMilliseconds);
            Console.Read();
        }
    }

    class AttributeRetriever {
        private static Dictionary<ICustomTypeDescriptor, PropertyDescriptor> _descriptorCache = new Dictionary<ICustomTypeDescriptor, PropertyDescriptor>();
        public static string GetAttribute<TModel, TProperty>(Expression<Func<TModel, TProperty>> exp, Type attributeType, string attributePropertyName) {
            var memberExpression = (MemberExpression)exp.Body;
            var propertyName = memberExpression.Member.Name;
            var containerType = memberExpression.Expression.Type;

            var typeDescriptor = new AssociatedMetadataTypeTypeDescriptionProvider(containerType).GetTypeDescriptor(containerType);
            PropertyDescriptor property;
            if(!_descriptorCache.TryGetValue(typeDescriptor, out property)) {
                property = typeDescriptor.GetProperties().Find(propertyName, true);
                _descriptorCache[typeDescriptor] = property;
            }
            
            var attributes = property.Attributes.Cast<Attribute>();
            var attribute = GetAttribute(attributes, attributeType);

            var value = GetAttributeValue(attribute, attributePropertyName);
            return value.ToString();
        }

        private static Dictionary<Type, PropertyInfo> _attributeCache = new Dictionary<Type, PropertyInfo>();
        private static object GetAttributeValue(Attribute attribute, string attributePropertyName) {
            var attributeType = attribute.GetType();
            PropertyInfo property;

            if(!_attributeCache.TryGetValue(attributeType, out property)) {
                property = attributeType.GetProperty(attributePropertyName, BindingFlags.Instance | BindingFlags.Public);
                _attributeCache[attributeType] = property;
            }

            return property.GetValue(attribute, null);
        }

        private static Attribute GetAttribute(IEnumerable<Attribute> attributes, Type attributeType) {
            return attributes.FirstOrDefault(x => x.GetType().Equals(attributeType));
        }
    }

    class Model {
        [Description("Namn")]
        [Privilege(Privilege.User)]
        public string Name { get; set; }
    }
    
    enum Privilege {
        Admin = 1,
        User
    }

    internal class PrivilegeAttribute : Attribute {
        public Privilege Privilege { get; set; }

        public PrivilegeAttribute(Privilege privilege) {
            Privilege = privilege;
        }
    }
}