package java_cup;

/** This class represents a shift action within the parse table. 
 *  The action simply stores the state that it shifts to and responds 
 *  to queries about its type.
 *
 * @version last updated: 11/25/95
 * @author  Scott Hudson
 */
public class shift_action extends parse_action {

    /*-----------------------------------------------------------*/
    /*--- Constructor(s) ----------------------------------------*/
    /*-----------------------------------------------------------*/

    /** Simple constructor. 
     * @param shft_to the state that this action shifts to.
     */
    public shift_action(lalr_state shft_to) throws internal_error {
        /* sanity check */
        if (shft_to == null)
            throw new internal_error("Attempt to create a shift_action to a null state");

        _shift_to = shft_to;
    }

    /*-----------------------------------------------------------*/
    /*--- (Access to) Instance Variables ------------------------*/
    /*-----------------------------------------------------------*/

    /** The state we shift to. */
    protected lalr_state _shift_to;

    /** The state we shift to. */
    public lalr_state shift_to() {
        return _shift_to;
    }

    /*-----------------------------------------------------------*/
    /*--- General Methods ---------------------------------------*/
    /*-----------------------------------------------------------*/

    /** Quick access to type of action. */
    @Override
    public int kind() {
        return SHIFT;
    }

    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

    /** Equality test. */
    public boolean equals(shift_action other) {
        return other != null && other.shift_to() == shift_to();
    }

    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

    /** Generic equality test. */
    @Override
    public boolean equals(Object other) {
        if (other instanceof shift_action)
            return equals((shift_action) other);
        else return false;
    }

    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

    /** Compute a hash code. */
    @Override
    public int hashCode() {
        /* use the hash code of the state we are shifting to */
        return shift_to().hashCode();
    }

    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

    /** Convert to a string. */
    @Override
    public String toString() {
        return "SHIFT(to state " + shift_to().index() + ")";
    }

    /*-----------------------------------------------------------*/

}
