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)

[StructLayout(LayoutKind.Explicit)]
public struct OneOf
{
    [FieldOffset(0)] public byte Tag;
    [FieldOffset(1)] public int Integer;
    [FieldOffset(1)] public short Short;
    [FieldOffset(1)] public bool Bool;
}

enum is also suitable tag type.

[StructLayout(LayoutKind.Explicit)]
public struct OneOf2
{
    [FieldOffset(0)] public Kind Tag;
    [FieldOffset(1)] public int Integer;
    [FieldOffset(1)] public short Short;
    [FieldOffset(1)] public bool Bool;
    public enum Kind : byte { UInt, Short, Bool }
}

Query

AccessorRequest(target) requests for IAccessor depending on type target.

// Create service
IService service = Services.Create(NetAccessorHandlers.Instance);
// Create container target
IContainerTarget target = new NetOneOf(typeof(OneOf));
// Create request
IRequestFor<IAccessor> request = new AccessorRequest(target);
// Issue request
IOneOfAccessor<OneOf> accessor = service.GetRequired<IRequest, IOneOfAccessor<OneOf>>(request);

OneOfAccessorRequest(target) requests for IOneOfAccessor<OneOf, Element>.

// Create service
IService service = Services.Create(NetAccessorHandlers.Instance);
// Create container target
IContainerTarget target = new NetOneOf(typeof(OneOf));
// Create request
IRequestFor<IOneOfAccessor> request = new OneOfAccessorRequest(target);
// Issue request
IOneOfAccessor<OneOf> accessor = service.GetRequired<IRequest, IOneOfAccessor<OneOf>>(request);

OneOfAccessorRequest is specifically a request for specific writers. Each can be assigned with explicit customization.

// Create service
IService service = Services.Create(NetAccessorHandlers.Instance);
// Create container target
IContainerTarget target = new NetOneOf(typeof(OneOf));
// Create request
IRequestFor<IOneOfAccessor> request = new OneOfAccessorRequest
{
    Constructor = new ConstructorRequest(target),
    Deconstructor = new DeconstructorRequest(target),
    DefaultConstructor = new DefaultConstructorRequest(target),
    Fields = new ContentAccessorsRequest(target),
    IsAssigned = new IsAssignedRequest(target),
    Unassign = new UnassignRequest(target),
    ContainerType = new ContainerTypeRequest(target),
    ContentType = new ContentTypeRequest(target),
};
// Issue request
IOneOfAccessor<OneOf> accessor = service.GetRequired<IRequest, IOneOfAccessor<OneOf>>(request);

Usage

.DefaultConstructor creates a oneof with default value.

OneOf oneOf = accessor.DefaultConstructor.Read();

.Constructor creates a oneof from enumerable of elements.

OneOf oneOf = accessor.Constructor.Read((0, (object)10));

.Deconstructor reads values as an enumerable.

OneOf oneOf = new OneOf { Tag = 0, Integer = 10 };
(int tag, object value) = accessor.Deconstructor.Read(ref oneOf);

.Fields contains one-of option types.

OneOf oneOf = default;
accessor.Fields[1].Writer.WriteAs<short, OneOf>(10, ref oneOf);
short value = accessor.Fields[1].Reader.ReadAs<OneOf, short>(oneOf);

.IsAssigned tests whether a oneof is assigned in container.

OneOf oneOf = new OneOf { Tag = 0, Integer = 10 };
bool nonNull = accessor.IsAssigned.Read(oneOf);

.Unassign removes oneof at container.

OneOf oneOf = new OneOf { Tag = 0, Integer = 10 };
accessor.Unassign.Write(default, ref oneOf);

Notes

Boxed value-types can be accessed as object.

// Create accessor
IOneOfAccessor<OneOf> accessor =
    Services.Create(NetAccessorHandlers.Instance)
    .GetRequiredService<IOneOfAccessor<OneOf>>();
// Create one-of in heap
object oneOf = new OneOf { Tag = 0, Integer = 10 };
// Assign case to box in heap
accessor.Fields[1].Writer.TypeCast<short, object>().Write((short)11, oneOf);

Full Example

Full example

using System.Runtime.InteropServices;
using Avalanche.Accessor;
using Avalanche.DataType;
using Avalanche.Service;
using Avalanche.Utilities;
using Avalanche.Writer;
using Microsoft.Extensions.DependencyInjection;
using static System.Console;

public class structlayoutattribute
{
    public static void Run()
    {
        {
            // <10>
            // Create service
            IService service = Services.Create(NetAccessorHandlers.Instance);
            // Create container target
            IContainerTarget target = new NetOneOf(typeof(OneOf));
            // Create request
            IRequestFor<IAccessor> request = new AccessorRequest(target);
            // Issue request
            IOneOfAccessor<OneOf> accessor = service.GetRequired<IRequest, IOneOfAccessor<OneOf>>(request);
            // </10>
        }
        {
            // <11>
            // Create service
            IService service = Services.Create(NetAccessorHandlers.Instance);
            // Create container target
            IContainerTarget target = new NetOneOf(typeof(OneOf));
            // Create request
            IRequestFor<IOneOfAccessor> request = new OneOfAccessorRequest(target);
            // Issue request
            IOneOfAccessor<OneOf> accessor = service.GetRequired<IRequest, IOneOfAccessor<OneOf>>(request);
            // </11>
        }
        {
            // <11B>
            // Create service
            IService service = Services.Create(NetAccessorHandlers.Instance);
            // Create container target
            IContainerTarget target = new NetOneOf(typeof(OneOf), typeof(object));
            // Create request
            IRequestFor<IOneOfAccessor> request = new OneOfAccessorRequest(target);
            // Issue request
            IOneOfAccessor<OneOf> accessor = service.GetRequired<IRequest, IOneOfAccessor<OneOf, object>>(request);
            // </11B>
        }
        {
            // <12>
            // Create service
            IService service = Services.Create(NetAccessorHandlers.Instance);
            // Create container target
            IContainerTarget target = new NetOneOf(typeof(OneOf));
            // Create request
            IRequestFor<IOneOfAccessor> request = new OneOfAccessorRequest
            {
                Constructor = new ConstructorRequest(target),
                Deconstructor = new DeconstructorRequest(target),
                DefaultConstructor = new DefaultConstructorRequest(target),
                Fields = new ContentAccessorsRequest(target),
                IsAssigned = new IsAssignedRequest(target),
                Unassign = new UnassignRequest(target),
                ContainerType = new ContainerTypeRequest(target),
                ContentType = new ContentTypeRequest(target),
            };
            // Issue request
            IOneOfAccessor<OneOf> accessor = service.GetRequired<IRequest, IOneOfAccessor<OneOf>>(request);
            // </12>
        }

        {
            IOneOfAccessor<OneOf, object> accessor = Services.Create(NetAccessorHandlers.Instance).GetRequiredService<IOneOfAccessor<OneOf, object>>();
            {
                // <51>
                OneOf oneOf = accessor.DefaultConstructor.Read();
                // </51>
            }
            {
                // <52>
                OneOf oneOf = accessor.Constructor.Read((0, (object)10));
                // </52>
            }
            {
                // <53>
                OneOf oneOf = new OneOf { Tag = 0, Integer = 10 };
                (int tag, object value) = accessor.Deconstructor.Read(ref oneOf);
                // </53>
            }
            {
                // <54>
                OneOf oneOf = default;
                accessor.Fields[1].Writer.WriteAs<short, OneOf>(10, ref oneOf);
                short value = accessor.Fields[1].Reader.ReadAs<OneOf, short>(oneOf);
                // </54>
            }
            {
                // <62>
                OneOf oneOf = new OneOf { Tag = 0, Integer = 10 };
                bool nonNull = accessor.IsAssigned.Read(oneOf);
                // </62>
            }
            {
                // <63>
                OneOf oneOf = new OneOf { Tag = 0, Integer = 10 };
                accessor.Unassign.Write(default, ref oneOf);
                // </63>
            }
        }
        {
            // <72>
            // Create accessor
            IOneOfAccessor<OneOf> accessor =
                Services.Create(NetAccessorHandlers.Instance)
                .GetRequiredService<IOneOfAccessor<OneOf>>();
            // Create one-of in heap
            object oneOf = new OneOf { Tag = 0, Integer = 10 };
            // Assign case to box in heap
            accessor.Fields[1].Writer.TypeCast<short, object>().Write((short)11, oneOf);
            // </72>
        }
    }

    // <100>
    [StructLayout(LayoutKind.Explicit)]
    public struct OneOf
    {
        [FieldOffset(0)] public byte Tag;
        [FieldOffset(1)] public int Integer;
        [FieldOffset(1)] public short Short;
        [FieldOffset(1)] public bool Bool;
    }
    // </100>

    // <101>
    [StructLayout(LayoutKind.Explicit)]
    public struct OneOf2
    {
        [FieldOffset(0)] public Kind Tag;
        [FieldOffset(1)] public int Integer;
        [FieldOffset(1)] public short Short;
        [FieldOffset(1)] public bool Bool;
        public enum Kind : byte { UInt, Short, Bool }
    }
    // </101>

}