Implementing cache correctly in a class library for use in an asp.net application

In my opinion, the best solution would have the following characteristics:

• Uses the available caching services provided by the platform trying to avoid writing your own.

• Does not couple your class library to System.Web, in order to have the layers coherent.

• But if the class library is running inside an ASP.NET application the solution should not require to bring another caching implementation on (for example, the Enterprise Library Caching Application Block), which requires additional configuration and setup.

So, I would use an IoC strategy in order to allow the class library to use different caching implementations, based on the environment it is running on.

Suppose you define your abstract caching contract as:

public interface ICacheService 
{
    AddItem(...);
}

You could provide an implementation based on System.Web:

public AspNetBasedCacheService : ICacheService
{
    AddItem(...)
    {
        // Implementation that uses the HttpContext.Cache object
    }
 }

And then have that implementation 'published' as singleton. Note that the difference with your original approach is that the singleton is just a reference to the ASP.NET cache service based implementation, instead of the full 'cache object'.

public class CacheServiceProvider 
{
    public static ICacheService Instance {get; set;}

}

You would have to initialize the caching implementation either by performing lazy initialization, or at application startup (in Global.asax.cs)

And every domain component would be able to use the published caching service without knowing that it is implemented based on System.Web.

// inside your class library:
ICacheService cache = CacheServiceProvider.Instance;
cache.AddItem(...);

I agree that it is probably not the simplest solution, but I'm aiming for taking advantage of the ASP.NET cache implementation without sacrificing code decoupling and flexibility.

I hope I understood your question right.