Question

I have following class

public abstract class Rule
    {
        protected Rule()
        {
            Nodes = new List<Node>();
        }
        public List<Node> Nodes { get; private set; }
        public int NumberOfElements { get; set; }

        public abstract Result<Rule> Validate(IEnumerable<Node> validUnits);

    }

now, also i have :

public class MinNumberOfCredits : Rule
{

   public override string ToString()
    {
        return string.Format(NumberOfElements);
    }

    public override Result<Rule> Validate(IEnumerable<Node> validUnits)
    {
        var totalCredits = validUnits.Sum(x => x.Credits);
        return NumberOfElements > totalCredits ? new Result<MinNumberOfCredits>(ResultMessage.Fail, NumberOfElements) : new Result<MinNumberOfCredits>();
    }
}

the problem is that my return type is Result<Rule> but in specific class i must return Result<MinNumberOfCredits>.

Answer 1

In C# you cannot have methods having the same name and parameters but different return types, so what you have in mind does just not work. There a various possible approaches to solve your problem, but they depend on your exact use case:

• Make Rule a generic type Rule<T> and change the return type of Validate to Result<T>.
• Extract commonialities of Result<Rule> and Result<MinNumberOfCredits> into an interface and return that one.
• …

I’m aware that all of those solutions will require further modifications. I just wanted to give you a direction to go.