C# 0 The Complete Reference

interface

. Thus, 

the

set

 accessor, for example, cannot be specified as private in an 

interface

.

Here is a rewrite of the 

ISeries

 interface and the 

ByTwos

 class that uses a property 

called

Next

 to obtain and set the next element in the series:

// Use a property in an interface.

using System;

public interface ISeries {

  // An interface property.

  int Next {

    get; // return the next number in series

    set; // set next number

  }

}

// Implement ISeries.

class ByTwos : ISeries {

  int val;

  public ByTwos() {

    val = 0;

  }

  // Get or set value.

  public int Next {

    get {

      val += 2;

      return val;

    }

    set {

      val = value;

    }

  }

}

// Demonstrate an interface property.

class SeriesDemo3 {

  static void Main() {

    ByTwos ob = new ByTwos();

    // Access series through a property.

    for(int i=0; i < 5; i++)

      Console.WriteLine("Next value is " + ob.Next);

    Console.WriteLine("\nStarting at 21");

    ob.Next = 21;

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    for(int i=0; i < 5; i++)

      Console.WriteLine("Next value is " + ob.Next);

  }

}

The output from this program is shown here:

Next value is 2

Next value is 4

Next value is 6

Next value is 8

Next value is 10

Starting at 21

Next value is 23

Next value is 25

Next value is 27

Next value is 29

Next value is 31

Interface Indexers

An interface can specify an indexer. A one-dimensional indexer declared in an interface has 

this general form:

// interface indexer

element-type

 this[int 

index

] {

   get;

   set;

}

As before, only 

get

 or 

set

 will be present for read-only or write-only indexers, respectively. 

Also, no access modifiers are allowed on the accessors when an indexer is declared in an 

interface

.

Here is another version of 

ISeries

 that adds a read-only indexer that returns the 

i

-th

element in the series.

// Add an indexer in an interface.

using System;

public interface ISeries {

  // An interface property.

  int Next {

    get; // return the next number in series

    set; // set next number

  }

  // An interface indexer.

  int this[int index] {

    get; // return the specified number in series

  }

}

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