PersistentMap/PersistentOrderedMap/TransientOrderedMap.cs

using System.Collections;

namespace PersistentOrderedMap;

public sealed class TransientOrderedMap<K, V, TStrategy> : BaseOrderedMap<K, V, TStrategy> where TStrategy : IKeyStrategy<K>
{
    // This is mutable, but we treat it as readonly for the ID generation logic usually.
    private OwnerId _transactionId;

    public TransientOrderedMap(Node<K> root, TStrategy strategy, int count) 
        : base(root, strategy, count) 
    {
        _transactionId = OwnerId.Next();
    }

    public void Set(K key, V value)
    {
        _root = BTreeFunctions.Set(_root, key, value, _strategy, _transactionId, out bool countChanged);
        if (countChanged) Count++;
    }

    public void Remove(K key)
    {
        _root = BTreeFunctions.Remove<K,V, TStrategy>(_root, key, _strategy, _transactionId, out bool removed);
        if (removed) Count--;
    }

    public PersistentOrderedMap<K, V, TStrategy> ToPersistent()
    {
        // 1. Create the snapshot by copying all relevant information
            
        var snapshot = new PersistentOrderedMap<K, V, TStrategy>(_root, _strategy, Count);

        // 2. Protect the snapshot from THIS TransientOrderedMap by getting a new ownerId 
        // so that future edits will be done by CoW
        _transactionId = OwnerId.Next();
            
        return snapshot;
    }
}