public sealed record Result<T>(T? Value, string? Error)
{
    public bool IsSuccess => Error is null;

    public static Result<T> Success(T value) => new(value, null);
    public static Result<T> Failure(string error) => new(default, error);
}

var result = Result<int>.Success(42);
Console.WriteLine(result.IsSuccess ? result.Value : result.Error);