A question about dictionaries of Dictionaries

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here is what I would like to do:

Dictionary<string,Dictionary<string, XxXxXx>> BoB;

where XxXxXx can be class A, class B, class C...etc
and {A,B,C}:Class Z

so that i can declare (roughly-Pseudo)

class Rusty
{

     private Dictionary<String,A> _a;
     private Dictionary<String,B> _b;
     private Dictionary<String,C> _c;

     public Dictionary<String,????> Lookup( identifier id)
     {
          switch(id)
          {
               case id.a: return _a;
               case id.b: return _b;
               case id.c: return _c;}
          }
     }
}

yet the closest I can get results in:
CS1502, CS0029, CS0039 X|

Cannot convert type 'System.Collections.Generic.Dictionary<string,ClassA>' to 'System.Collections.Generic.Dictionary<string,ClassZ>' via a reference conversion, boxing conversion, unboxing conversion, wrapping conversion, or null type conversion

..basically says that what i have above can't be done..

couldn't find a decent reference for this type of "issue":confused:

any ideas?

As per aspdevdotnet's suggestion(thank you)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Jumba
{
    class A:Z
    {
    }
    class B:Z
    {
    }
    class C:Z
    {
    }
    class Z
    {
    }
    class Y 
    {
        Dictionary<string, Dictionary<string,Z>> Bob = new Dictionary<string,Dictionary<string,Z>>();
        Dictionary<string, A> _a = new Dictionary<string,A>();
        Dictionary<string, B> _b = new Dictionary<string,B>();
        Dictionary<string, C> _c = new Dictionary<string,C>();
        public Y() 
        {
            //Error	4	Argument '2': cannot convert from 'System.Collections.Generic.Dictionary<string,Jumba.A>' to 'System.Collections.Generic.Dictionary<string,Jumba.Z>'	
            Bob.Add("a",_a);
            //Error	6	Argument '2': cannot convert from 'System.Collections.Generic.Dictionary<string,Jumba.A>' to 'System.Collections.Generic.Dictionary<string,Jumba.Z>'	
            Bob.Add("b",_b);
            //Error	8	Argument '2': cannot convert from 'System.Collections.Generic.Dictionary<string,Jumba.A>' to 'System.Collections.Generic.Dictionary<string,Jumba.Z>'	
            Bob.Add("c",_c);
        }
        public Dictionary<string, Z> Retrieve(string str) 
        {
            Object alpha = Bob[str];
            //Error	15	Cannot implicitly convert type 'Jumba.A' to 'System.Collections.Generic.Dictionary<string,Jumba.Z>'	
            if (alpha is A){return (alpha as A)}
        
        }
    }

}

Posted 6-Dec-09 11:29am

ely_bob

Updated 6-Dec-09 12:10pm

v3

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4 solutions

Solution 2

Regarding your updated sample. You seem to have missed the point. This is what you want:

C#

//  Your dictionaries will be of value Z (so, A, B, and C instances can be placed in it).
Dictionary<string, Z> _a = new Dictionary<string,Z>();
Dictionary<string, Z> _b = new Dictionary<string,Z>();
Dictionary<string, Z> _c = new Dictionary<string,Z>();

// Your retrieve method will return a dictionary, not a Z derived instance.
public Dictionary<string, Z> Retrieve(string str)
{
    return Bob[str];
}

Or, you could have 3 Retrieve methods if you want to do the work for the user of this class:

C#

public A RetrieveA(string str) { return Bob["a"][str] as A; }
public B RetrieveB(string str) { return Bob["b"][str] as B; }
public C RetrieveC(string str) { return Bob["c"][str] as C; }

Posted 6-Dec-09 12:26pm

AspDotNetDev

Solution 1

Since C# is strongly typed, your types are clashing. What you can do is have classes A, B, and C derive from som common parent class (say, AlphaClass), then create a dictionary of that type. Or, since all classes derive from the Object class, you could just use Object instead of AlphaClass:

C#

// A, B, and C should derive from AlphaClass.
Dictionary<string, Dictionary<string, AlphaClass>> BoB;
// Or, just use Object, since they already derive from that class.
Dictionary<string, Dictionary<string, Object>> BoB;

When you get one of the items from the dictionary, you can then just check its type and convert it to that type:

C#

Object alpha = BoB["A"]["someKey"];
if(alpha is A) (alpha as A).SomeAMethod();

Posted 6-Dec-09 11:49am

AspDotNetDev

Solution 4

:-D Yes interface usage is the answer.. I just realized it on my way into work.. :)

I've started a Article about this, and hopefull will have it up soone thanks.

Posted 7-Dec-09 5:16am

ely_bob

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Amgad Fahmi · Accepted Answer · 2009-12-06T19:50:00

This exactly what the interfaces do in .Net
Make an interface represent the common stuff between all the classes Ex

public interface IInterface
       {
           int number{get; set;}
           void doSomething();
       }

Then implement this interface in each class

public classA : IInterface
{
//implementation goes here 
}

And the calling step (if you want to retrieve the object only)

public IInterface Retrieve(string str)
      {
          return Bob[str];
      }

Or of if you want to retireve the dictionary

public Dictionary<string,IInterface  > Retrieve(string str)
      {
          return new Dictionary<string, IInterface>().Add(f, Bob[str]);
      }

Or for better solution use Linq (my favourite one )

public Dictionary<string,IInterface> Retrieve(string str) 
        {
 return Bob.Where(c => c.Key == str ).ToDictionary(c => c.Key, c => c.Value);
}

hope i could help