StructLayoutAttribute

[StructLayout(LayoutKind.Explicit)] is another way to formulate an one-of type. Each field must have [FieldOffset(X)] attribute.

The first field at [FieldOffset(0)] indicates tag type. Its length and name can be anything. All other fields must have non zero offset. Note that referable types must be positioned at 8 byte alignments. (Avalanche.DataType.Net.dll)

// Create service
IService service = Services.Create(NetTypeHandlers.Instance);
// Create request
DataTypeRequest<NetOneOf> request = new(typeof(MyOneOf));
// Query 
IOneOfType datatype = service.GetRequired<DataTypeRequest<NetOneOf>, IOneOfType>(request);

[StructLayout(LayoutKind.Explicit)]
public struct MyOneOf
{
    [FieldOffset(0)] public byte Tag;
    [FieldOffset(1)] public uint Int;
    [FieldOffset(1)] public ushort Short;
    [FieldOffset(1)] public bool Bool;
}

oneoftype+MyOneOf, docs, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null : IOneOfType
├── Fields[0] = Int : IFieldType
│   └── Value = uint32 : IIntegerType
├── Fields[1] = Short : IFieldType
│   └── Value = uint16 : IIntegerType
└── Fields[2] = Bool : IFieldType
    └── Value = bool : IIntegerType

enum is also suitable tag type.

[StructLayout(LayoutKind.Explicit)]
public struct MyOneOf
{
    [FieldOffset(0)] public OneOfKind Kind;
    [FieldOffset(1)] public uint Int;
    [FieldOffset(1)] public ushort Short;
    [FieldOffset(1)] public bool Bool;
    public enum OneOfKind : byte { Int, Short, Bool }
}

oneoftype+MyOneOf, docs, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null : IOneOfType
├── Fields[0] = Int : IFieldType
│   └── Value = uint32 : IIntegerType
├── Fields[1] = Short : IFieldType
│   └── Value = uint16 : IIntegerType
└── Fields[2] = Bool : IFieldType
    └── Value = bool : IIntegerType

Full Example

Full example

using System.Runtime.InteropServices;
using Avalanche.DataType;
using Avalanche.Identity;
using Avalanche.Service;
using static System.Console;

public class structlayoutattribute
{
    public static void Run()
    {
        {
            // <05>
            // Create service
            IService service = Services.Create(NetTypeHandlers.Instance);
            // Create request
            DataTypeRequest<NetOneOf> request = new(typeof(MyOneOf));
            // Query 
            IOneOfType datatype = service.GetRequired<DataTypeRequest<NetOneOf>, IOneOfType>(request);
            // </05>
            // Print
            WriteLine(datatype.PrintTree());
        }
    }

    // <101>
    [StructLayout(LayoutKind.Explicit)]
    public struct MyOneOf
    {
        [FieldOffset(0)] public byte Tag;
        [FieldOffset(1)] public uint Int;
        [FieldOffset(1)] public ushort Short;
        [FieldOffset(1)] public bool Bool;
    }
    // </101>

    static class _102
    {
        // <102>
        [StructLayout(LayoutKind.Explicit)]
        public struct MyOneOf
        {
            [FieldOffset(0)] public OneOfKind Kind;
            [FieldOffset(1)] public uint Int;
            [FieldOffset(1)] public ushort Short;
            [FieldOffset(1)] public bool Bool;
            public enum OneOfKind : byte { Int, Short, Bool }
        }
        // </102>
    }

    static class _103
    {
        // <103>
        [StructLayout(LayoutKind.Explicit)]
        public sealed class MyOneOf
        {
            [FieldOffset(0)] public byte Tag;
            [FieldOffset(1)] public uint Int;
            [FieldOffset(1)] public ushort Short;
            [FieldOffset(1)] public bool Bool;
        }
        // </103>
    }

    static class _104
    {
        // <104>
        [StructLayout(LayoutKind.Explicit)]
        public sealed class MyOneOf
        {
            [FieldOffset(0)] public OneOfKind Kind;
            [FieldOffset(1)] public uint Int;
            [FieldOffset(1)] public ushort Short;
            [FieldOffset(1)] public bool Bool;
            public enum OneOfKind : byte { Int, Short, Bool }
        }
        // </104>
    }

}