Can StructureMap return a Special Case?

Question

I want to have StructureMap return a Special Case called "None" for a certain instance.

Say I Have this class MyUser which is scoped as HttpContext. I want to have a nested, dreived class None (ie. MyUser.None) which is returtned for the type MyUser when there is no HttpContext (for example, like in bootstrapping, Application_Start() etc).

This would mean that certain calls could check for the Special Case type instead of null (more readable) like

if(value is MyUser.None)
  // do special case things
else
  // do normal case things

What SM config do I need to achieve this? I have tried the ConditionallyUse method without much success. I keep getting NullReferenceExceptionS throwing from within SM itself.

Answer 1

Turns out I had underlying SM configuration issues.

I am using the ConditionallyUse method still however:

        For<User>().ConditionallyUse(config =>
            {
                config.If(ctx => ctx.GetInstance<HttpContextBase>().User == null)
                    .ThenIt.Is.Type<User.None>();
                config.TheDefault.Is.Type<User>();
            });

I had to be more careful about NullReferenceExceptionS from within SM - my underlying cause it seems was a scoping issue.. specifically how I was wanting to access a HttpContext scoped instance in a test. I'm now using the HybridHttpOrThreadLocalScoped() config and being more careful by using TryGetInstance() where appropiate instead of GetInstance().