IServiceProvider Extension Method

I love extension methods, 'nuff said:

public static class ServiceProviderExtension
{
    public static T GetService<T>(this IServiceProvider provider) where T: class
    {
        return provider.GetService(typeof(T)) as T;
    }

    public static K GetService<T, K>(this IServiceProvider provider)
        where T : class, K
        where K : class
    {
        return provider.GetService() as K;
    }

    public static K GetService<K>(this IServiceProvider provider, Type type)
        where K : class
    {
        return provider.GetService(type) as K;
    }

    public static K GetService<K>(this IServiceProvider provider, string type)
        where K : class
    {
        return provider.GetService(Type.GetType(type)) as K;
    }
}