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Posted 25 Jan 2012

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Multiple Indexers in C#

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5.00/5 (6 votes)
25 Jan 2012CPOL
An elegant programmatic solution for having multiple indexers in C#
In C#, you can't have multiple indexers like you can do in VB, so the following code is not supported:

SQL
class C
{
    public Foo Foos[int i]
    {
        ...
    }
    public Bar Bars[int i]
    {
        ...
    }
}


On the other hand, exposing internal IEnumerable is not always a desired solution (because you want to limit access to your internal collections - that's why indexers are for in the first place.)

Workaround



I came up with this simple class that you can add to your code:

C#
public class IndexProperty<T,I>
   {
       private Func<I,T> getter;
       private Action<I, T> setter;

       public IndexProperty(Func<I, T> g, Action<I, T> s)
       {
           if (g == null || s == null)
               throw new ArgumentNullException();
           getter = g;
           setter = s;
       }

       public T this[I index]
       {
           get
           {
               return getter(index);
           }
           set
           {
               setter(index, value);
           }
       }
   }


Now, you can add multiple indexers to your class, but make sure you initialize the indexers properly. The following example demonstrates how to expose multiple indexers:

C#
public class MyClass
   {
       private List<string> myList = new List<string>();
       public MyClass()
       {
           myList.AddRange(new string[]{"1","2","3"});
           // Init the IndexProperty with your methods (or lambdas)
           this.Keys=new IndexProperty<string,int>(
               i=> myList[i],
               (j,val)=> myList[j]=val);
       }

       public IndexProperty<string,int> Keys { get; set; }
   }


The following code demonstrates how your class can be used:

C#
static void SampleMethod()
       {
           MyClass c = new MyClass();
           c.Keys[0] = "value";
       }

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Sion Cohen
Architect
Israel Israel
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Comments and Discussions

 
GeneralGood work around Pin
Dean Oliver25-Jan-12 18:55
MemberDean Oliver25-Jan-12 18:55 
QuestionInteresting Pin
PIEBALDconsult25-Jan-12 14:45
professionalPIEBALDconsult25-Jan-12 14:45 
AnswerRe: Interesting Pin
Sion Cohen25-Jan-12 22:50
MemberSion Cohen25-Jan-12 22:50 
GeneralRe: Interesting Pin
PIEBALDconsult26-Jan-12 2:08
professionalPIEBALDconsult26-Jan-12 2:08 
GeneralRe: Interesting Pin
Sion Cohen26-Jan-12 3:17
MemberSion Cohen26-Jan-12 3:17 
GeneralRe: Interesting Pin
PIEBALDconsult30-Jan-12 3:11
professionalPIEBALDconsult30-Jan-12 3:11 

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