code: //==============================================================================
  //	
  //	Copyright (c) 2016-
  //	Authors:
  //	* Steffen Maercker <maercker@tcs.inf.tu-dresden.de> (TU Dresden)
  //	
  //------------------------------------------------------------------------------
  //	
  //	This file is part of PRISM.
  //	
  //	PRISM is free software; you can redistribute it and/or modify
  //	it under the terms of the GNU General Public License as published by
  //	the Free Software Foundation; either version 2 of the License, or
  //	(at your option) any later version.
  //	
  //	PRISM is distributed in the hope that it will be useful,
  //	but WITHOUT ANY WARRANTY; without even the implied warranty of
  //	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  //	GNU General Public License for more details.
  //	
  //	You should have received a copy of the GNU General Public License
  //	along with PRISM; if not, write to the Free Software Foundation,
  //	Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  //	
  //==============================================================================
  
  package common.iterable;
  
  import java.util.Iterator;
  import java.util.Optional;
  import java.util.OptionalDouble;
  import java.util.OptionalInt;
  import java.util.OptionalLong;
  import java.util.PrimitiveIterator;
  
  /**
   * Base class for an iterator that ranges over a single element,
   * static helpers for common primitive iterators.
   */
  public abstract class SingletonIterator<T> implements Iterator<T>
  {
  	public static class Of<T> extends SingletonIterator<T>
  	{
  		private Optional<T> element;
  
  		public Of(T element)
  		{
  			this.element = Optional.of(element);
  		}
  
  		@Override
  		public boolean hasNext()
  		{
  			return element.isPresent();
  		}
  
  		@Override
  		public T next()
  		{
  			Optional<T> result = element;
  			element = Optional.empty();
  			return result.get();
  		}
  	}
  
  	public static class OfInt extends SingletonIterator<Integer> implements PrimitiveIterator.OfInt
  	{
  		private OptionalInt element;
  
  		public OfInt(int element)
  		{
  			this.element = OptionalInt.of(element);
  		}
  
  		@Override
  		public boolean hasNext()
  		{
  			return element.isPresent();
  		}
  
  		@Override
  		public int nextInt()
  		{
  			OptionalInt result = element;
  			element = OptionalInt.empty();
  			return result.getAsInt();
  		}
  	}
  
  	public static class OfLong extends SingletonIterator<Long> implements PrimitiveIterator.OfLong
  	{
  		private OptionalLong element;
  
  		public OfLong(Long element)
  		{
  			this.element = OptionalLong.of(element);
  		}
  
  		@Override
  		public boolean hasNext()
  		{
  			return element.isPresent();
  		}
  
  		@Override
  		public long nextLong()
  		{
  			OptionalLong result = element;
  			element = OptionalLong.empty();
  			return result.getAsLong();
  		}
  	}
  
  	public static class OfDouble extends SingletonIterator<Double> implements PrimitiveIterator.OfDouble
  	{
  		private OptionalDouble element;
  
  		public OfDouble(double element)
  		{
  			this.element = OptionalDouble.of(element);
  		}
  
  		@Override
  		public boolean hasNext()
  		{
  			return element.isPresent();
  		}
  
  		@Override
  		public double nextDouble()
  		{
  			OptionalDouble result = element;
  			element = OptionalDouble.empty();
  			return result.getAsDouble();
  		}
  	}
  }
  