DefaultImplementationAttribute.cs

using System;
using System.Collections.Generic;
using System.Reflection;
 
namespace Waher.Runtime.Inventory
{
    [AttributeUsage(AttributeTargets.Interface | AttributeTargets.Class, AllowMultiple = false, Inherited = true)]
    public class DefaultImplementationAttribute : Attribute
    {
        private static readonly Dictionary<Type, Type> defaultImplementationOverrides = new Dictionary<Type, Type>();
        private readonly Type type;
 
        public DefaultImplementationAttribute(Type Type)
        {
            if (Type is null)
                throw new ArgumentException("Type cannot be null.", nameof(Type));
 
            this.type = Type;
        }
 
        public Type Type => this.type;
 
        public static void RegisterDefaultImplementation(Type From, Type To)
        {
            lock (defaultImplementationOverrides)
            {
                if (defaultImplementationOverrides.ContainsKey(From))
                    throw new InvalidOperationException("Default implemnentation already registered.");
 
                defaultImplementationOverrides[From] = To;
            }
        }
 
        public static bool UnregisterDefaultImplementation(Type From, Type To)
        {
            lock (defaultImplementationOverrides)
            {
                if (defaultImplementationOverrides.TryGetValue(From, out Type To2) && To == To2)
                    return defaultImplementationOverrides.Remove(From);
                else
                    return false;
            }
        }
 
        public static bool TryGetDefaultImplementation(Type Type, out Type DefaultImplementation)
        {
            lock (defaultImplementationOverrides)
            {
                if (defaultImplementationOverrides.TryGetValue(Type, out DefaultImplementation))
                    return true;
            }
 
            TypeInfo TI = Type.GetTypeInfo();
            DefaultImplementationAttribute Attr = TI.GetCustomAttribute<DefaultImplementationAttribute>(true);
 
            if (!(Attr is null))
            {
                DefaultImplementation = Attr.Type;
                return true;
            }
            else
                return false;
        }
    }
}