Abstract base class or Interface? Neither seem right.

Question

Given the following code:

using System.Collections.Generic;
static class Program {
 static void Main() {
  bar Bar = new bar();
  baz Baz = new baz();
  System.Console.WriteLine(
   "We have {0} bars, rejoice!", bar.Cache.Count);
 }
}

public abstract class foo {
 public static List<foo> Cache = new List<foo>(); 
}

public class bar : foo {
 public bar() { Cache.Add(this); }
}
public class baz : foo {
 public baz() { Cache.Add(this); }
}

You get the (somewhat expected) output "We have 2 bars, rejoice!".

This is fabulous, we now have twice as many places to have our beer (apparently), but what I really want is for each class to have it's own cache. The reason I don't want to just implement this cache in the subclass is because I also have some methods in my abstract class that needs to be able to operate on the cache (namely, to iterate over all of them). Is there a way to do this? I've looked at using an interface for foo, but the interface doesn't allow static members to be defined as part of the interface.

Answer 1

Here's your answer:

using System;
using System.Collections.Generic;
static class Program
{
    static void Main()
    {
        var bar = new Bar();
        var baz = new Baz();
        System.Console.WriteLine(
                "We have {0} bars, rejoice!", Bar.Cache.Count);

        bar.PrintList();
        baz.PrintList();
    }
}

public abstract class Foo<T>
{
    public static List<T> Cache = new List<T>();

    public void PrintList()
    {
        foreach(var item in Cache)
        {
            Console.WriteLine(item);

        }
    }
}

public class Bar : Foo<Bar>
{
    public Bar() { Cache.Add(this); }
}
public class Baz : Foo<Baz>
{
    public Baz() { Cache.Add(this); }
}

Answer 2

try this:

using System.Collections.Generic;
using System;
static class Program
{
  static void Main()
  {
    Bar bar = new Bar();
    Baz baz = new Baz();
    System.Console.WriteLine(
            "We have {0} bars, rejoice!", bar.Cache.Count);
    System.Console.ReadKey();
  }
}

public abstract class Foo
{
  public Foo()
  {
    Cache = new List<string>();
  }
  public List<String> Cache { get; set; }
}

public class Bar : Foo
{
  public Bar() 
  { 
    Cache.Add("Bar"); 
  }
}
public class Baz : Foo
{
  public Baz() { Cache.Add("Baz"); }
}

Sorry I had to change the casing.. It was making my head explode

Answer 3

public abstract class foo {
    public abstract List<foo> Cache { get; }

    protected static Dictionary<Type, List<foo>> InnerCache = new Dictionary<Type, List<foo>>(); 
}

public class bar : foo {
    public override List<foo> Cache { 
       get { return foo.InnerCache[typeof(bar)]; } 
    }

    public bar() { Cache.Add(this); }
}

public class baz : foo {
    public override List<foo> Cache { 
       get { return foo.InnerCache[typeof(baz)]; } 
    }

    public baz() { Cache.Add(this); }
}

Answer 4

Use a generic base class parameterized with the subclass:

using System.Collections;
using System.Collections.Generic;

static class Program
{
    static void Main()
    {
        bar Bar = new bar();
        baz Baz = new baz();
        System.Console.WriteLine(
                "We have {0} bars, rejoice!", Bar.GetCache().Count);
    }
}

public abstract class foo<T>
{
    private static List<foo<T> > Cache = new List<foo<T> >();

    public IList GetCache()
    {
        return Cache;
    }
}

public class bar : foo<bar>
{
    public bar() { GetCache().Add(this); }
}
public class baz : foo<baz>
{
    public baz() { GetCache().Add(this); }
}

Answer 5

Each derived class of foo should define how/where to get a cache, so each can (potentially) have its own cache. Methods in foo can refer to GetCache() without the implementation being known.

public abstract class foo
{
    public abstract ICache GetCache();

    public void DoSomethingToCache()
    {
        ICache cache = this.GetCache();
        cache.DoSomething();
    }
}

public class bar : foo
{
    public static ICache BarCache = new FooCache();

    public override ICache GetCache()
    {
        return bar.BarCache;
    }
}

public class FooCache : ICache { }