Question

Given the following interface:

public interface IFoo
{
    bool Foo(Person a, Person b);
}

and the following two implementations of the above:

public class KungFoo : IFoo
{
    public bool Foo(Person a, Person b)
    {
        if (a.IsAmateur || b.IsAmateur) // common logic
          return true;
        return false;
    }
}

public class KongFoo : IFoo
{
    public bool Foo(Person a, Person b)
    {
        if (a.IsAmateur || b.IsAmateur) // common logic
          return false;
        return true;
    }
}

where should I place the “common logic” (as commented in the code) so it is in just one place (e.g. as a Func) and does not need to be repeated (as is the case above) for multiple implementations?

Note that the example above is very trivial but the real-life “common logic” is more complicated and the Foo() method does something useful!

I hope the question is clear (and not already been answered elsewhere – I did do a search) but feel free to probe me for more details if required.

Answer 1

In a common abstract class:

public interface IFoo
{
    bool Foo(Person a, Person b);
}

public abstract class FooBase : IFoo
{
    public virtual bool Foo(Person a, Person b)
    {
        if (a.IsAmateur || b.IsAmateur) // common logic
          return true;
        return false;
    }
}

public class KungFoo : FooBase
{

}

public class KongFoo : FooBase
{
    public override bool Foo(Person a, Person b)
    {
        // Some other logic if the common logic doesn't work for you here
    }
}