gistfile1.cs

using System.Web.Mvc;
using Core.Web;
using Machine.Specifications;

namespace Core.Specs.Web
{
    [Subject(typeof(TempDataExtensions))]
    public class when_setting_success_flash
    {
        Establish context = () =>
        {
            _tempData = new TempDataDictionary();
        };

        Because of = () => _tempData.Flash(FlashResult.Success);

        It should_contain_a_success_flash = () =>
        {
            var flash = (Flash) _tempData["FLASH"];
            flash.Result.ShouldEqual(FlashResult.Success);
        };

        static TempDataDictionary _tempData;
    }

    [Subject(typeof(TempDataExtensions))]
    public class when_setting_warning_flash
    {
        Establish context = () =>
        {
            _tempData = new TempDataDictionary();
        };

        Because of = () => _tempData.Flash(FlashResult.Warning);

        It should_contain_a_warning_flash = () =>
        {
            var flash = (Flash)_tempData["FLASH"];
            flash.Result.ShouldEqual(FlashResult.Warning);
        };

        static TempDataDictionary _tempData;
    }

    [Subject(typeof(TempDataExtensions))]
    public class when_setting_error_flash
    {
        Establish context = () =>
        {
            _tempData = new TempDataDictionary();
        };

        Because of = () => _tempData.Flash(FlashResult.Error);

        It should_contain_a_error_flash = () =>
        {
            var flash = (Flash)_tempData["FLASH"];
            flash.Result.ShouldEqual(FlashResult.Error);
        };

        static TempDataDictionary _tempData;
    }

    [Subject(typeof(TempDataExtensions))]
    public class when_setting_flash_with_custom_messages
    {
        Establish context = () =>
        {
            _tempData = new TempDataDictionary();
            _messages = new [] { new FlashMessage("Hello"), new FlashMessage("World") };
        };

        Because of = () => _tempData.Flash(FlashResult.Error, _messages);

        It should_contain_the_flash_messages = () =>
        {
            var flash = (Flash)_tempData["FLASH"];
            flash.Messages.ShouldContainOnly(_messages);
        };

        static TempDataDictionary _tempData;
        static FlashMessage[] _messages;
    }

}

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using System.Collections.Generic;

namespace Core.Web
{
    public class Flash
    {
        public Flash(FlashResult result, IEnumerable<FlashMessage> messages)
        {
            Result = result;
            Messages = messages;
        }

        public FlashResult Result { get; private set; }
        public IEnumerable<FlashMessage> Messages { get; private set; }
    }
}

===========================================================

namespace Core.Web
{
    public struct FlashMessage
    {
        readonly string _message;

        public FlashMessage(string message)
        {
            _message = message;
        }

        public static explicit operator string(FlashMessage instance)
        {
            return instance._message;
        }
    }
}

===========================================================

namespace Core.Web
{
    public enum FlashResult
    {
        Success = 0,
        Warning = 1,
        Error = 2
    }
}

===========================================================

using System.Collections.Generic;
using System.Web.Mvc;

namespace Core.Web
{
    public static class TempDataExtensions
    {
        public static void Flash(this TempDataDictionary tempDataDictionary, FlashResult result)
        {
            tempDataDictionary.Flash(result, new List<FlashMessage>());
        }

        public static void Flash(this TempDataDictionary tempDataDictionary, FlashResult result, IEnumerable<FlashMessage> messages)
        {
            if (tempDataDictionary.ContainsKey("FLASH")) tempDataDictionary.Remove("FLASH");
            tempDataDictionary.Add("FLASH", new Flash(result, messages));
        }
    }
}