CancellablePipeline.cs

namespace Pipelines
{
    using System;
    using System.Collections.Generic;
    using System.Linq;

    public class CancellablePipeline<TPipelineDelegateType, TReturnType>
        where TReturnType : class
    {
        public CancellablePipeline()
        {
            if (!typeof(Delegate).IsAssignableFrom(typeof(TPipelineDelegateType)))
            {
                throw new ArgumentException("TPipelineDelegateType must be of a delegate type", "TPipelineDelegateType");
            }

            this.pipelineItems = new List<TPipelineDelegateType>();
        }

        private List<TPipelineDelegateType> pipelineItems;
        public IEnumerable<TPipelineDelegateType> PipelineItems 
        { 
            get
            {
                return this.pipelineItems.AsReadOnly();
            } 
        }

        public TReturnType Invoke(params object[] args)
        {
            TReturnType returnValue = null;

            using (var enumerator = this.PipelineItems.Select(i => i as Delegate).GetEnumerator())
            {
                while (returnValue == null && enumerator.MoveNext())
                {
                    returnValue = enumerator.Current.DynamicInvoke(args) as TReturnType;
                }
            }

            return returnValue;
        }

        public void AddItemToStartOfPipeline(TPipelineDelegateType item)
        {
            this.InsertItemAtPipelineIndex(0, item);
        }

        public void AddItemToEndOfPipeline(TPipelineDelegateType item)
        {
            this.pipelineItems.Add(item);
        }

        public void InsertItemAtPipelineIndex(int index, TPipelineDelegateType item)
        {
            this.pipelineItems.Insert(index, item);
        }
    }

}