Enumerator problem

Floydian · August 20th, 2009, 11:47 AM

Hello,

This question relates to chapter 5 in the book. I'm getting an error when building the HelloCollection code.

'HelloCollection.Enumerator' does not contain a
constructor that takes '0' arguments

Code:

public class HelloCollection : IEnumerable {
			public IEnumerator GetEnumerator() {
				Enumerator enumerator = new Enumerator();
				return enumerator;
			}
			public class Enumerator : IEnumerator, IDisposable {
				private int state;
				private object current;
				
				public Enumerator(int state) {
					this.state = state;
				}

Clearly, the Enumerator constructor here does require one argument, and clearly the Enumerator is instantiated without passing in an argument. The book shows it this way, and I could not find a code example for this in the downloads. (The download has the HelloCollection that comes first in the book, the second version of it appears to be missing)

Should I be instantiating the Enumerator using a value of say 0?

Floydian · September 25th, 2009, 04:21 PM

Well, I'm slowly making my way through the book. It'd be fantastic to know for sure if this is or is not an error in the book...

Also, the errata form has about 20 some fields to fill in. Come on, I'm not giving you my phone number (a required field ffs) just so that I can post an error in ***your*** book...

Here is possibly another error:

Page 814
string [] lines = new string[nLines];

Doesn't that need to use parenthesis instead of square brackets? new string(nLines);

Cheers

irProject · December 7th, 2009, 03:35 AM

you can write your Enumerator class like this:

Code:

public class Enumerator : IEnumerator, IDisposable 
{
   private int state;
   private object current;

   public Enumerator(int state) 
   {
      this.state = state;
   }

   public Enumerator() :this(0)
   {}
}

because you don't have defined parameterless constructor in your class, when you try to create a new object of this class in 'Enumerator enumerator = new Enumerator();' command you get and exception.

Bob Bedell · December 7th, 2009, 05:28 PM

Quote:

Here is possibly another error:

Page 814
string [] lines = new string[nLines];

Doesn't that need to use parenthesis instead of square brackets? new string(nLines);

C# uses brackets.

Code:


// verbose
int[] a = newint[4];
for (int i = 0; i < a.Length; ++i)
{
   a[i] = (i + 1) * 2;
}
 
// compact
int[] b = newint[] { 2, 4, 6, 8 };
//ultra-compact
int[] c = { 2, 4, 6, 8 };