InstanceCache.cs

#region License
// Copyright (c) Jeremy Skinner (http://www.jeremyskinner.co.uk)
// 
// Licensed under the Apache License, Version 2.0 (the "License"); 
// you may not use this file except in compliance with the License. 
// You may obtain a copy of the License at 
// 
// http://www.apache.org/licenses/LICENSE-2.0 
// 
// Unless required by applicable law or agreed to in writing, software 
// distributed under the License is distributed on an "AS IS" BASIS, 
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
// See the License for the specific language governing permissions and 
// limitations under the License.
// 
// The latest version of this file can be found at http://FluentValidation.codeplex.com
#endregion

namespace ServiceStack.FluentValidation.Internal
{
    using System;
    using System.Collections.Generic;

    /// <summary>
    /// Instancace cache.
    /// TODO: This isn't actually completely thread safe. It would be much better to use ConcurrentDictionary, but this isn't available in Silverlight/WP7.
    /// </summary>
    public class InstanceCache {
        readonly Dictionary<Type, object> cache = new Dictionary<Type, object>();
        readonly object locker = new object();

        /// <summary>
        /// Gets or creates an instance using Activator.CreateInstance
        /// </summary>
        /// <param name="type">The type to instantiate</param>
        /// <returns>The instantiated object</returns>
        public object GetOrCreateInstance(Type type) {
            return GetOrCreateInstance(type, Activator.CreateInstance);
        }

        /// <summary>
        /// Gets or creates an instance using a custom factory
        /// </summary>
        /// <param name="type">The type to instantiate</param>
        /// <param name="factory">The custom factory</param>
        /// <returns>The instantiated object</returns>
        public object GetOrCreateInstance(Type type, Func<Type, object> factory) {
            object existingInstance;

            if(cache.TryGetValue(type, out existingInstance)) {
                return existingInstance;
            }

            lock(locker) {
                if (cache.TryGetValue(type, out existingInstance)) {
                    return existingInstance;
                }

                var newInstance = factory(type);
                cache[type] = newInstance;
                return newInstance;
            }
        }
    }
}