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ActionScript allows defining dynamic classes which facilitate adding public properties and methods to them at run time. Internally these classes maintain a hash table for storing the properties and methods added at run-time.

Since ActionScript 3, a Dictionary class is available which allows for creating <key, value> mappings but it lacks the interface that, for example, C++’s std::map provides.

Adding properties at run-time can be leveraged to implement a very simple hashmap which, unfortunately, is not available in ActionScript.

Below is a class which can be used as a hashmap.

//HashMap.as
 
import mx.collections.ArrayCollection;
 
public dynamic class HashMap
{
	private var size_:Number = 0;
	public function get size():Number
	{
		return size_;
	}
 
	/**
	 * Inserts a new  pair to the map
	 */
	public function insert(key:String, value:Object):void
	{
		// Only increment counter if the
		// item is not already in the map.
		if (!this.hasOwnProperty(key))
		{
			size_++;
		}
		this[key] = value;
	}
 
	/**
	 * Removes an element from the map
	 */
	public function erase(key:String):void
	{
		// Only decrement counter if the item is in the map.
		if (this[key])
		{
			size_--;
		}
		delete this[key];
	}
 
	/**
	 * Removes all elements from the map
	 */
	public function clear():void
	{
		for (var key:String in this)
		{
			delete this[key];
		}
		size_ == 0;
	}
 
	/**
	 * Returns the element identified by key `key`
	 */
	public function getItem(key:String):Object
	{
		return this[key];
	}
 
	/**
	 * Returns the element at index `index`
	 */
	public function getIemAt(index:int):*
	{
		var i:int = 0;
		for (var key:String in this)
		{
			if (i == index)
			{
				return this[key];
			}
			++i;
		}
		return null;
	}
 
	/**
	 * Check if the map contains any elements
	 */
	public function empty():Boolean
	{
		return size == 0;
	}
}

UPDATE (11/01/2010):

Thanks to a suggestion by Craig W, I have updated the code of HashMap class. The `size()` method has been replaced by property `size`. Also the `erase()` and `clear()` methods have been updated. They now use the `delete` operator to remove properties instead of setting the properties to `null` which was causing the `size()` method to return incorrect result.

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