C# 0 The Complete Reference

len

 for its storage. 

Length

 defines 

only a 

get

 accessor, which means that it is read-only. Thus, 

Length

 can be read, but not 

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changed. To prove this to yourself, try removing the comment symbol preceding this line 

in the program:

// fs.Length = 10; // Error, illegal!

When you try to compile, you will receive an error message stating that 

Length

 is read-only.

Although the addition of the 

Length

 property improves 

FailSoftArray

, it is not the only 

improvement that properties can make. The 

ErrFlag

 member is also a prime candidate for 

conversion into a property since access to it should also be limited to read-only. Here is the 

final improvement of 

FailSafeArray

. It creates a property called 

Error

 that uses the original 

ErrFlag

variable as its storage, and 

ErrFlag

 is made private to 

FailSoftArray

.

// Convert ErrFlag into a property.

using System;

class FailSoftArray {

  int[] a; // reference to underlying array

  int len; // length of array

  bool ErrFlag; // now private

  // Construct array given its size.

  public FailSoftArray(int size) {

    a = new int[size];

    len = size;

  }

  // Read-only Length property.

  public int Length {

    get {

      return len;

    }

  }

  // Read-only Error property.

  public bool Error {

    get {

      return ErrFlag;

    }

  }

  // This is the indexer for FailSoftArray.

  public int this[int index] {

    // This is the get accessor.

    get {

      if(ok(index)) {

        ErrFlag = false;

        return a[index];

      } else {

        ErrFlag = true;

        return 0;

      }

    }

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