Serialize HashSet into a binary file

using var writer = new BinaryWriter(someStream, Encoding.Whatever);

foreach (var v in hashSet)
    writer.Write((int)v);

using var writer = new BinaryWriter(someStream, Encoding.Whatever);

foreach (var v in hashSet)
    writer.Write((int)v);

using System.Runtime.InteropServices;

namespace Program {
    enum Test {
        A = 1,
        B = 2,
        C = 3
    }

    [StructLayout(LayoutKind.Explicit)]
    class Program {
        static void Main() {
            HashSet<Test> set = new HashSet<Test>();

            set.Add(Test.A);
            set.Add(Test.C);
            set.Add(Test.B);

            unsafe {
                UInt64 start = (UInt64) (UInt64*) &set;
                UInt64 size = (UInt64) sizeof(HashSet<Test>);
                UInt64 end = start + size;
                int size2 = Marshal.SizeOf(set);
                Console.WriteLine($"Addr: 0x{start:X} - 0x{end:X} | {size}");
                int a = 5; // breakpoint for debugging
            }
        }
    }
}

using System.Runtime.InteropServices;

namespace Program {
    enum Test {
        A = 1,
        B = 2,
        C = 3
    }

    [StructLayout(LayoutKind.Explicit)]
    class Program {
        static void Main() {
            HashSet<Test> set = new HashSet<Test>();

            set.Add(Test.A);
            set.Add(Test.C);
            set.Add(Test.B);

            unsafe {
                UInt64 start = (UInt64) (UInt64*) &set;
                UInt64 size = (UInt64) sizeof(HashSet<Test>);
                UInt64 end = start + size;
                int size2 = Marshal.SizeOf(set);
                Console.WriteLine($"Addr: 0x{start:X} - 0x{end:X} | {size}");
                int a = 5; // breakpoint for debugging
            }
        }
    }
}

private struct Entry
{
    public int HashCode;
    /// <summary>
    /// 0-based index of next entry in chain: -1 means end of chain
    /// also encodes whether this entry _itself_ is part of the free list by changing sign and subtracting 3,
    /// so -2 means end of free list, -3 means index 0 but on free list, -4 means index 1 but on free list, etc.
    /// </summary>
    public int Next;
    public T Value;
}

private struct Entry
{
    public int HashCode;
    /// <summary>
    /// 0-based index of next entry in chain: -1 means end of chain
    /// also encodes whether this entry _itself_ is part of the free list by changing sign and subtracting 3,
    /// so -2 means end of free list, -3 means index 0 but on free list, -4 means index 1 but on free list, etc.
    /// </summary>
    public int Next;
    public T Value;
}

pointer (4 or 8 bytes in length)
pointer (4 or 8)
int (4)
int (4)
int (4)
int (4)

pointer (4 or 8 bytes in length)
pointer (4 or 8)
int (4)
int (4)
int (4)
int (4)

private struct Entry
{
    public int HashCode;
    /// <summary>
    /// 0-based index of next entry in chain: -1 means end of chain
    /// also encodes whether this entry _itself_ is part of the free list by changing sign and subtracting 3,
    /// so -2 means end of free list, -3 means index 0 but on free list, -4 means index 1 but on free list, etc.
    /// </summary>
    public int Next;
    public T Value;
}

private struct Entry
{
    public int HashCode;
    /// <summary>
    /// 0-based index of next entry in chain: -1 means end of chain
    /// also encodes whether this entry _itself_ is part of the free list by changing sign and subtracting 3,
    /// so -2 means end of free list, -3 means index 0 but on free list, -4 means index 1 but on free list, etc.
    /// </summary>
    public int Next;
    public T Value;
}

struct Example {
    int a;
    std::vector<float> b;
    double c;
    std::string d;
    int e;
};

struct Example {
    int a;
    std::vector<float> b;
    double c;
    std::string d;
    int e;
};