public class DependencyResolver
{
    // Fields
    private IDependencyResolver _current;
    private CacheDependencyResolver _currentCache;
    private static DependencyResolver _instance;

    // Methods
    static DependencyResolver();
    public DependencyResolver();
    public void InnerSetResolver(object commonServiceLocator);
    public void InnerSetResolver(IDependencyResolver resolver);
    public void InnerSetResolver(Func<Type, object> getService, Func<Type, IEnumerable<object>> getServices);
    public static void SetResolver(object commonServiceLocator);
    public static void SetResolver(IDependencyResolver resolver);
    public static void SetResolver(Func<Type, object> getService, Func<Type, IEnumerable<object>> getServices);

    // Properties
    public static IDependencyResolver Current { get; }
    internal static IDependencyResolver CurrentCache { get; }
    public IDependencyResolver InnerCurrent { get; }
    internal IDependencyResolver InnerCurrentCache { get; }

    // Nested Types
    private sealed class CacheDependencyResolver : IDependencyResolver
    {
        // Fields
        private readonly ConcurrentDictionary<Type, object> _cache;
        private readonly ConcurrentDictionary<Type, IEnumerable<object>> _cacheMultiple;
        private readonly IDependencyResolver _resolver;

        // Methods
        public CacheDependencyResolver(IDependencyResolver resolver);
        public object GetService(Type serviceType);
        public IEnumerable<object> GetServices(Type serviceType);
    }

    private class DefaultDependencyResolver : IDependencyResolver
    {
        // Methods
        public DefaultDependencyResolver();
        public object GetService(Type serviceType);
        public IEnumerable<object> GetServices(Type serviceType);
    }

    private class DelegateBasedDependencyResolver : IDependencyResolver
    {
        // Fields
        private Func<Type, object> _getService;
        private Func<Type, IEnumerable<object>> _getServices;

        // Methods
        public DelegateBasedDependencyResolver(Func<Type, object> getService, Func<Type, IEnumerable<object>> getServices);
        public object GetService(Type type);
        public IEnumerable<object> GetServices(Type type);
    }
}