Result type to hold a result of either success or failure in Unity C#

Result.cs

using System;

namespace MyNamespace
{
    /// holds an either succeeded or failed result
    // need latest C# version to use <out T, out E> instead
    public interface Result<T, E> where E : Exception
    {
        public bool OK { get; }

        public static Failure<T, E> Failed(E error)
        {
            return new Failure<T, E>(error);
        }
        public static Success<T, E> Succeeded(T content)
        {
            return new Success<T, E>(content);
        }

        // Fold without returning a value
        public void OnComplete(Action<T> onSuccess, Action<E> onFailure)
        {
            Fold<bool>(t => { onSuccess(t); return true; }, t => { onFailure(t); return false; });
        }

        public R Fold<R>(Func<T, R> onSuccess, Func<E, R> onFailure);
    }

    public class Failure<T, E> : Result<T, E> where E : Exception
    {

        public bool OK
        {
            get { return false; }
        }

        public readonly E Error;

        internal Failure(E error)
        {
            Error = error;
        }
        public R Fold<R>(Func<T, R> onSuccess, Func<E, R> onFailure)
        {
            return onFailure(Error);
        }
    }
    public class Success<T, E> : Result<T, E> where E : Exception
    {

        public readonly T Content;
        public bool OK
        {
            get { return true; }
        }
        internal Success(T content)
        {
            Content = content;
        }

        public R Fold<R>(Func<T, R> onSuccess, Func<E, R> onFailure)
        {
            return onSuccess(Content);
        }
    }
}