Is it a dictionary? Is it a value? Yes!

DictWithDefault.cs

public class DictWithDefault<TKey, TValue>
{
    public readonly TValue DefaultValue;
    private readonly Dictionary<TKey, TValue> values = new Dictionary<TKey, TValue>();

    public DictWithDefault(TValue defaultValue = default)
    {
        this.DefaultValue = defaultValue;
    }

    public TValue this[TKey key]
    {
        get => this.values.TryGetValue(key, out var val) ? val : this.DefaultValue;
        set => this.values[key] = value;
    }

    public static implicit operator TValue(DictWithDefault<TKey, TValue> dict) => dict.DefaultValue;

    public static implicit operator DictWithDefault<TKey, TValue>(TValue art) =>
        new DictWithDefault<TKey, TValue>(art);

    public static bool operator ==(DictWithDefault<TKey, TValue> thisOne, TValue thatOne) =>
        EqualityComparer<TValue>.Default.Equals(thatOne, thisOne != null ? thisOne.DefaultValue : default);

    public static bool operator !=(DictWithDefault<TKey, TValue> thisOne, TValue thatOne) => !(thisOne == thatOne);

    public override bool Equals(object obj)
    {
        return ReferenceEquals(this, obj) ||
               obj is DictWithDefault<TKey, TValue> dict
               && Equals(this, dict);
    }

    protected bool Equals(DictWithDefault<TKey, TValue> other)
    {
        return EqualityComparer<TValue>.Default.Equals(this.DefaultValue, other.DefaultValue) && Equals(this.values, other.values);
    }

    public override int GetHashCode()
    {
        unchecked
        {
            return (EqualityComparer<TValue>.Default.GetHashCode(this.DefaultValue) * 397) ^ (this.values != null ? this.values.GetHashCode() : 0);
        }
    }
}

You should press ctrl + A -> ctrl+shift+tab

Fair enough. ctrl+shift+tab didn't do anything though, so I just pressed shift+tab.

Oh my bad. ctrl+shift+tab is a browser thing lol.