package de.unisiegen.tpml.core.expressions ;


/**
 * Instances of this class represent the <code>Assign</code> operator in the
 * expression hierarchy.
 * 
 * @author Benedikt Meurer
 * @author Christian Fehler
 * @version $Rev:1053 $
 * @see Deref
 * @see Ref
 * @see BinaryOperator
 */
public final class Assign extends BinaryOperator
{
  /**
   * The assign operator exception string.
   */
  private static final String HANDLED = "assign operator must be handled by the interpreter" ; //$NON-NLS-1$


  /**
   * The unused string.
   */
  private static final String UNUSED = "unused" ; //$NON-NLS-1$


  /**
   * The keyword <code>:=</code>.
   */
  private static final String COLONEQUAL = ":=" ; //$NON-NLS-1$


  /**
   * The caption of this {@link Expression}.
   */
  private static final String CAPTION = Expression.getCaption ( Assign.class ) ;


  /**
   * Allocates a new <code>Assign</code> operator.
   */
  public Assign ( )
  {
    super ( COLONEQUAL , PRIO_ASSIGN ) ;
  }


  /**
   * Allocates a new <code>Assign</code> operator.
   * 
   * @param pParserStartOffset The start offset of this {@link Expression} in
   *          the source code.
   * @param pParserEndOffset The end offset of this {@link Expression} in the
   *          source code.
   */
  public Assign ( int pParserStartOffset , int pParserEndOffset )
  {
    this ( ) ;
    this.parserStartOffset = pParserStartOffset ;
    this.parserEndOffset = pParserEndOffset ;
  }


  /**
   * {@inheritDoc} The assign operator does not a machine equivalent like the
   * arithmetic or relational operators, but instead operates on a store. So
   * applying an assign operator to its operands must be implemented in the
   * interpreter. This method simply throws
   * {@link UnsupportedOperationException} on every invokation.
   * 
   * @throws UnsupportedOperationException on every invokation.
   * @see BinaryOperator#applyTo(Expression, Expression)
   */
  @ SuppressWarnings ( UNUSED )
  @ Override
  public Expression applyTo ( @ SuppressWarnings ( UNUSED )
  Expression pExpression1 , @ SuppressWarnings ( UNUSED )
  Expression pExpression2 ) throws BinaryOperatorException
  {
    throw new UnsupportedOperationException ( HANDLED ) ;
  }


  /**
   * {@inheritDoc}
   * 
   * @see Expression#clone()
   */
  @ Override
  public Assign clone ( )
  {
    return new Assign ( ) ;
  }


  /**
   * {@inheritDoc}
   */
  @ Override
  public String getCaption ( )
  {
    return CAPTION ;
  }
}