Two way dictionary

TwoWayDictionary.cs

// This is a version of System.Collections.Generic.Dictionary<TKey, TValue> where both types can act as keys and values.
// For example, you could have a TwoWayDictionary<string, int>. This would be able to look up ints by string, but
// it would ALSO be able to look up strings by int.
// All the code in this class is O(1) except for the seeded constructors.

// you are free to use and modify this code for anything, full licence terms at the end of the file.

using System.Collections.Generic;
using System.Linq;

public class TwoWayDictionary<T1, T2>
{
    Dictionary<T1, T2> _Forwards = new Dictionary<T1, T2>();
    Dictionary<T2, T1> _Backwards = new Dictionary<T2, T1>();
    
    public IReadOnlyDictionary<T1, T2> Forwards => _Forwards;
    public IReadOnlyDictionary<T2, T1> Backwards => _Backwards;
    
    public IEnumerable<T1> Set1 => Forwards.Keys;
    public IEnumerable<T2> Set2 => Backwards.Keys;
    
    
    public TwoWayDictionary()
    {
        _Forwards = new Dictionary<T1, T2>();
        _Backwards = new Dictionary<T2, T1>();
    }
    
    public TwoWayDictionary(int capacity)
    {
        _Forwards = new Dictionary<T1, T2>(capacity);
        _Backwards = new Dictionary<T2, T1>(capacity);
    }
    
    public TwoWayDictionary(Dictionary<T1, T2> initial)
    {
        _Forwards = initial;
        _Backwards = initial.ToDictionary(kvp => kvp.Value, kvp => kvp.Key);
    }
    
    public TwoWayDictionary(Dictionary<T2, T1> initial)
    {
        _Backwards = initial;
        _Forwards = initial.ToDictionary(kvp => kvp.Value, kvp => kvp.Key);
    }
    
    
    public T1 this[T2 index]
    {
        get => _Backwards[index];
        set
        {
            if (_Backwards.TryGetValue(index, out var removeThis))
                _Forwards.Remove(removeThis);
    
            _Backwards[index] = value;
            _Forwards[value] = index;
        }
    }
    
    public T2 this[T1 index]
    {
        get => _Forwards[index];
        set
        {
            if (_Forwards.TryGetValue(index, out var removeThis))
                _Backwards.Remove(removeThis);
    
            _Forwards[index] = value;
            _Backwards[value] = index;
        }
    }
    
    public int Count => _Forwards.Count;
    
    public bool Contains(T1 item) => _Forwards.ContainsKey(item);
    public bool Contains(T2 item) => _Backwards.ContainsKey(item);
    
    public bool Remove(T1 item)
    {
        if (!this.Contains(item))
            return false;
    
        var t2 = _Forwards[item];
    
        _Backwards.Remove(t2);
        _Forwards.Remove(item);
    
        return true;
    }
    
    public bool Remove(T2 item)
    {
        if (!this.Contains(item))
            return false;
    
        var t1 = _Backwards[item];
    
        _Forwards.Remove(t1);
        _Backwards.Remove(item);
    
        return true;
    }
    
    public void Clear()
    {
        _Forwards.Clear();
        _Backwards.Clear();
    }
}


//        DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE 
//                    Version 2, December 2004 
//
// Copyright (C) 2004 Sam Hocevar <sam@hocevar.net> 
//
// Everyone is permitted to copy and distribute verbatim or modified 
// copies of this license document, and changing it is allowed as long 
// as the name is changed. 
//
//            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE 
//   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 
//
//  0. You just DO WHAT THE FUCK YOU WANT TO.