Iterator for custom Hashtable C#

Question

I need to provide an iterator for my custom fixed sized hashtable class, I am storing the data in an array of linkedlist.

class HashTableNode<T1, T2>
{
    public T1 Key { get; set; }
    public T2 Value { get; set; }
}
class HashTableClass<T1, T2>
{
    public LinkedList<HashTableNode<T1, T2>>[] elements;
    const int defaultSize = 10000;
    
    public HashTableIterator<T1, T2> GetIterator()
    {
         return new HashTableIterator<T1, T2>(this);
    }
}

class HashTableIterator<T1, T2> 
{
    //need to implement this
}

For the iterator I need following functionalities:

• HasNext() // tells if there is an element at current iterator position
• Current // returns the value stored at current iterator position
• MoveNext() // moves the iterator to next position

HashTableClass<int, string> hashtable = new HashTableClass<int, string>();
//Iterator will be used like this
HashTableIterator<int, string> iterator = hashtable.GetIterator();
while(iterator.HasNext())
{
    Console.Write(iterator.Current);
    iterator.MoveNext();
}

Answer 1

In .NET there is stadard IEnumerable pattern. Better to stay with this implementation. If you want to expose only values, you can do the following

public class HashTableNode<T1, T2>
{
    public T1 Key { get; set; }
    public T2 Value { get; set; }
}

public class HashTableClass<T1, T2>: IEnumerable<T2>
{
    public LinkedList<HashTableNode<T1, T2>>[] elements;
    const int defaultSize = 10000;

    public IEnumerator<T2> GetEnumerator()
    {
        return elements.SelectMany(l => l).Select(e => e.Value).GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

Or you can introduce methods which returns IEnumerable

public IEnumerable<T2> GetValues()
{
    return elements.SelectMany(l => l).Select(e => e.Value);
}

Or using yield return

public IEnumerable<T2> GetValues()
{
    foreach (var list in elements)
    {
        foreach (var node in list)
            yield return node.Value;
    }
}

In all cases, you can use foreach for your collection:

var hashTable = ...

foreach (var value in hashTable)
{
    ...
}

foreach (var value in hashTable.GetValues())
{
    ...
}

If you want to get "iterator" which is called IEnumerator in .NET, you can call IEnumerable.GetEnumerator()

using var enumerator = hashTable.GetEnumerator();
// or
using var enumerator = hashTable.GetValues().GetEnumerator();

while (enumerator.MoveNext())
{
    Console.Write(enumerator.Current);
}