I have the following class with a generic type parameter.

public class ContentService<T> : IContentService where T : DataString, new()
{       
    public ContentService(IEnvironment environment, 
                          ILogger logger)
    {
        _environment = environment;
        _logger = logger;
    }
...
}

DataString is an abstract class and I want Structure Map to use a concrete implementation (XmlDataString) whenever my application creates an instance of ContentService. Structure Map is already injecting concrete implementations of IEnvironment and ILogger when I do this:

Version 1:

_contentService = ObjectFactory.GetInstance<ContentService<DataString>>();

... but when I step through, ContentService is created with a type parameter of DataString, not XmlDataString. I have these three entries in web.config that set default instances:

• IEnvironment -> TestEnvironment
• ILogger -> Log4NetLogger
• DataString -> XmlDataString

The Structure Map site has this to say about generics, but I can't seem to relate that example to my actual problem.

This approach works, but I'm losing the auto wiring of the constructor arguments and it looks quite ugly: Version 2:

Type typeOfDataString = ObjectFactory.GetInstance<DataString>().GetType();
Type genericClass = typeof(ContentService<>);
Type constructedClass = genericClass.MakeGenericType(typeOfDataString);
_contentService = (IContentService)Activator.CreateInstance(constructedClass, 
            ObjectFactory.GetInstance<IEnvironment>(), 
            ObjectFactory.GetInstance<ILogger>());

Can anyone tell me what I'm doing wrong in the first version, or how I might improve the second version?

• c#
• generics
• abstract-class
• structuremap

First, when you write ObjectFactory.GetInstance<ContentService<DataString>>(), you can't get ContentService<XmlDataString> back, because that's a different, incompatible type.

But it seems you actually want IContentService, so write that: ObjectFactory.GetInstance<IContentService>(). This will return the implementation of IContentService that you registered, so you should do that: register ContentService<XmlDataString> for IContentService. The fact that you have XmlDataString registered for DataString has nothing to do with this.

If you have problems representing the generic type ContentService<XmlDataString> in web.config, I think using the .Net representation of generic types (and not that of C#) should work. In your case, that would be something like ContentService`1[[XmlDataString]], probably with added namespaces and possibly assemblies too.