UnionWithMethods.cs

public class Union<TOne, TOther>
{
    private readonly TOne _toneValue;
    private readonly TOther _totherValue;
    private readonly UnionType _type;

    public Union(TOne value)
    {
        _toneValue = value;
        _type = UnionType.TOne;
    }

    public Union(TOther value)
    {
        _totherValue = value;
        _type = UnionType.TOther;
    }

    public void Switch(Action<TOne> actionTOne, Action<TOther> actionTOther)
    {
        switch (_type)
        {
            case UnionType.TOne:
                actionTOne(_toneValue);
                break;
            case UnionType.TOther:
                actionTOther(_totherValue);
                break;
        }
    }

    public TResult Match<TResult>(Func<TOne, TResult> funcTOne, Func<TOther, TResult> funcTOther)
    {
        switch (_type)
        {
            case UnionType.TOne:
                return funcTOne(_toneValue);
            case UnionType.TOther:
                return funcTOther(_totherValue);
        }

        throw new InvalidOperationException();
    }

    enum UnionType
    {
        TOne,
        TOther
    }
}