Nesting base classes in c#

Question

I have 3 classes, two inherit from 1:

public class Employee {
    private virtual double getBonus() { ... }
    private virtual double getSalary() { ... }
}

public class Nepotism : Employee {
    private double getBonus() { ... }
}

public class Volunteer : Employee {
    private double getSalary() { ... }
}

So the question is sometimes there will be a Volunteer who gets the Nepotism bonus - is there some way to write the constructors to allow overriding/nesting the base class like this:

Employee Bill = new Volunteer(new Nepotism());

I'm thinking something like:

public class Volunteer : Employee {
    private Employee _nest;
    public Volunteer(Employee nest) 
        : base() {
        _nest = nest;
        // now what?
    }
}

Basically I want some objects to have the overrides from both classes.

I would like to avoid writing the override methods to check for nested classes.

getSalary() {
    return (nest != null) ? nest.salary : salary; // I want to avoid this if I can
}

How can I do this? Am I on the right track? Am I off the rails?

Answer 1

Instead of subclassing, you might want to consider using the Decorator Pattern.

It provides an alternative to subclassing, and it useful when you may need to add "multiple" pieces of additional functionality to a single instance of a class, which is exactly the scenario.

Answer 2

If an object can be both classes at once, then you may need to rethink how you're doing your inheritance.

It seems to me that if a Volunteer can sometimes get a Nepotism bonus, then really, your Volunteer class should have a getBonus() method, and this method really belongs in the base class. It would return zero for most volunteers, but occasionally it wouldn't - there's nothing wrong with that.

Answer 3

I think you are trying to use inheritance in an ill-advised way. This approach creates a mess of dependences and oddball business rules, which results in a rigid architecture that is hard to use and maintain.

If calculating an employees salary is dependent upon the Employee as well as "bonus traits", then it would be better to separate all three things from each other:

interface IBonusTrait
{
    decimal ApplyBonus(Employee employee, decimal currentTotal);
}

class Employee
{
    // ...

    public decimal BaseSalary { get; set; }
    public IList<IBonusTrait> BonusTraits { get; set; }
}

class SalaryCalculator
{
    public decimal CalculateSalary(Employee employee)
    {
        decimal totalSalary = employee.BaseSalary;
        foreach (IBonusTrait bonusTrait in employee.BonusTraits)
        {
            totalSalary = bonusTrait.ApplyBonus(employee, totalSalary);
        }

        return totalSalary;
    }
}