[Question] deserialization of immutable collection

[aPlacuzzi]

Hi all,

With C#8 they introduce immutable collections like ImmutableList, ImmutableDictionary, and go on.

The deserialization of these collections seems to be actually not supported.

What is the best way to add this extension to the deserializer?

[NiccoMlt]

Same problem here

[aPlacuzzi]

I'm already here, but with a solution (or at least a workaround) for ImmutableList.
I took inspiration from CollectionNodeDeserializer.

/// <summary>
/// Node deserializer to deserialize <see cref="IImmutableList{T}"/>.
/// </summary>
internal class ImmutableListNodeDeserializer : INodeDeserializer
{
	/// <inheritdoc/>
	public bool Deserialize(IParser reader, Type expectedType, Func<IParser, Type, object> nestedObjectDeserializer, out object value)
	{
		if (!(expectedType.IsInterface && expectedType.IsGenericType && expectedType.GetGenericTypeDefinition() == typeof(IImmutableList<>)))
		{
			value = null;
			return false;
		}
		const string methodName = "AddRange";
		var itemType = expectedType.GetGenericArguments()[0];
		var list = (Activator.CreateInstance(typeof(List<>).MakeGenericType(itemType)) as IList;
		if (list == null)
		{
			value = null;
			return false;
		}
		DeserializeHelper(itemType, reader, nestedObjectDeserializer, list, canUpdate: true);
		value = Activator.CreateInstance(typeof(ImmutableList<>).MakeGenericType(itemType), true);
		value = value.GetType()
			.GetMethod(methodName)
			.Invoke(value, new[] { list });
		return true;
	}

	private static void DeserializeHelper(Type tItem, IParser parser, Func<IParser, Type, object> nestedDeserializer, IList result, bool canUpdate)
	{
		parser.Consume<SequenceStart>();
		while (!parser.TryConsume<SequenceEnd>(out var _))
		{
			var current = parser.Current;

			var value = nestedDeserializer(parser, tItem);
			if (value is IValuePromise promise)
			{
				if (canUpdate)
				{
					var index = result.Add(tItem.GetTypeInfo().IsValueType ? Activator.CreateInstance(tItem) : null);
					promise.ValueAvailable += v => result[index] = TypeConverter.ChangeType(v, tItem, CultureInfo.InvariantCulture);
				}
				else
				{
					throw new ForwardAnchorNotSupportedException(
						current?.Start ?? Mark.Empty,
						current?.End ?? Mark.Empty,
						"Forward alias references are not allowed because this type does not implement IList<>");
				}
			}
			else
			{
				result.Add(TypeConverter.ChangeType(value, tItem, CultureInfo.InvariantCulture));
			}
		}
	}
}

[somegenericdev]

Any updates on this? This is something it would be really nice to have.

[EdwardCooke]

We don't have it built in, we welcome PR's though.