Scope.java

package ecologylab.collections;

import java.util.HashMap;
import java.util.Map;

import ecologylab.generic.Debug;

/**
 * A lexical Scope of bindings from names to values. Lexical Scopes can be nested. However, bind
 * operations are only performed on the current Scope. Lookup operations chain through parents, as
 * necessary, when a binding is not found locally.
 */
public class Scope<T> extends HashMap<String, T>
{
	protected Map<String, T>	parent;

	/**
	 * Create a Scope with no parent, using default HashMap size and loadFactor.
	 */
	public Scope()
	{

	}

	/**
	 * Create a lexical Scope, chained to a parent Scope for resolving lookup/get. Use the default
	 * HashMap size and loadFactor.
	 * 
	 * @param parent
	 */
	public Scope(Map<String, T> parent)
	{
		this.parent = parent;
	}

	/**
	 * Create a Scope with no parent, using the specified HashMap size and default loadFactor.
	 * 
	 * @param size
	 */
	public Scope(int size)
	{
		super(size);
	}

	/**
	 * Create a lexical Scope, chained to a parent Scope for resolving lookup/get. Use the specified
	 * HashMap size and default loadFactor.
	 * 
	 * @param size
	 */
	public Scope(Map<String, T> parent, int size)
	{
		super(size);
		this.parent = parent;
	}

	/**
	 * Create a Scope with no parent, using the specified HashMap size and loadFactor.
	 * 
	 * @param size
	 * @param loadFactor
	 */
	public Scope(int size, float loadFactor)
	{
		super(size, loadFactor);
	}

	/**
	 * Create a lexical Scope, chained to a parent Scope for resolving lookup/get. Use the specified
	 * HashMap size and loadFactor.
	 * 
	 * @param parent
	 * @param size
	 * @param loadFactor
	 */
	public Scope(Map<String, T> parent, int size, float loadFactor)
	{
		super(size, loadFactor);
		this.parent = parent;
	}

	/**
	 * Lookup an object in this.
	 * 
	 * @param name
	 * 
	 * @return The object associated with this name, found in the registry, or null if there is none.
	 */
	@Override
	public T get(Object name)
	{
		T result = super.get(name);
		Map<String, T> operativeParent = parent;
		return (result != null) ? result : ((operativeParent != null) ? operativeParent.get(name)
				: null);
	}

	/**
	 * Enable this Scope to inherit bindings from a parent, by setting the parent instance variable in
	 * this.
	 * 
	 * @param newParent
	 */
	public void setParent(Map<String, T> newParent)
	{
		Map<String, T> thisParent = this.parent;
		if (thisParent != null)
			Debug.warning(this, "Setting parent to " + newParent + " but it was already " + thisParent);

		this.parent = newParent;
	}

	/**
	 * The chained parent Map used for resolving lookup/get operations, if they cannot be resolved in
	 * this.
	 * 
	 * @return The parent instance variable in this.
	 */
	public Map<String, T> operativeParent()
	{
		return this.parent;
	}

	@Override
	public String toString()
	{
		String parentMsg = (parent == null) ? "" : "\n\t -> " + parent.toString();
		return sizeMsg() + parentMsg;
	}

	public String sizeMsg()
	{
		return "[Scope] w " + size() + " elements. ";
	}

	/**
	 * 
	 * @return A String with all the name value pairs in this, for debugging.
	 */
	public String dump()
	{
		StringBuilder result = new StringBuilder();
		result.append("DUMP");
		dump(result, "\t");
		return result.toString();
	}

	private void dump(StringBuilder result, String prefix)
	{
		result.append('\n').append(prefix).append(sizeMsg());
		dumpThis(result, prefix);
		if (parent != null)
			((Scope) parent).dump(result, prefix + "\t");
	}

	public void dumpThis(StringBuilder result, String prefix)
	{
		for (String key : this.keySet())
		{
			result.append(prefix).append(key).append("\t: ").append(get(key)).append('\n');
		}
	}

	private static final long	serialVersionUID	= 5840169416933494011L;
}