NestedSet.java

package kodkod.engine.fol2sat;

import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

/**
 * Implements a data structure that contains sets of values at different nesting levels. 
 *   
 * @author aleks
 */
@SuppressWarnings("unchecked")
public class NestedSet<T> implements Iterable<T> {

    private final NestedSet<T> parent; 
    private final Set<T> elems;

    private NestedSet(NestedSet<T> parent) {
        this(parent, new HashSet<T>());
    }
    
    private NestedSet(NestedSet<T> parent, Set<T> elems) {
        this.parent = parent;
        this.elems = elems;
    }
    
    public NestedSet<T> createNested() {
        return new NestedSet<T>(this); 
    }
    
    public void add(T elem)                          { this.elems.add(elem); }
    public void addAll(Collection<? extends T>elems) { this.elems.addAll(elems); }
    public NestedSet<T> parent()                     { return parent; }
    @Override public Iterator<T> iterator()          { return elems.iterator(); }

    @SuppressWarnings("rawtypes")
    private static final NestedSet EMPTY = new NestedSet(null);    
    public static <T> NestedSet<T> empty() { return (NestedSet<T>) EMPTY; }
    
}