public static class MaybeExtensions
{
    public static Maybe<T> ToMaybe<T>(this T input) where T : class
    {
        return new Maybe<T>(input);
    }

    public static Maybe<TResult> Get<TInput, TResult>(this Maybe<TInput> maybe, Func<TInput, TResult> func)
        where TInput : class
        where TResult : class
    {
        var result = maybe.HasValue ? new Maybe<TResult>(func(maybe.Value)) : Maybe<TResult>.None;
        return result;
    }

    public static Maybe<TInput> If<TInput>(this Maybe<TInput> maybe, Func<TInput, bool> func) where TInput : class
    {
        return maybe.HasValue && func(maybe.Value)
            ? maybe
            : Maybe<TInput>.None;
    }

    public static TResult Return<TInput, TResult>(this Maybe<TInput> maybe, Func<TInput, TResult> func, TResult defaultValue) where TInput : class
    {
        return maybe.HasValue
            ? func(maybe.Value)
            : defaultValue;
    }
}

public sealed class Maybe<T> where T : class
{
    public static Maybe<T> None = new Maybe<T>(default(T));

    public T Value { get; set; }

    public bool HasValue
    {
        get { return Value != null && !Value.Equals(default(T)); }
    }

    public Maybe(T value)
    {
        Value = value;
    }
}