Unions

If your data needs to contain a lot of different fields for different cases, consider using a union.

using System.Runtime.InteropServices;

public enum TargetType : byte
{
    Point,
    Region,
    Entity,
}

[StructLayout (LayoutKind.Explicit, Pack = 1)]
public struct Target
{
    [FieldOffset(0)] public readonly TargetType TargetType;
    [FieldOffset(1)] public readonly Vector3 Point;
    [FieldOffset(1)] public readonly Region Region;
    [FieldOffset(1)] public readonly Entity Entity;
}

Here, Point, Region and Entity occupy the same memory space. The [FieldOffset] attribute takes a number of bytes as argument. since our enum TargetType has a size of 1 byte, the 3 fields are offset by 1 byte in memory.

To learn more about unions, see http://jacksondunstan.com/articles/3325