ExpressionVisitor.php

<?php

/*
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 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * This software consists of voluntary contributions made by many individuals
 * and is licensed under the MIT license. For more information, see
 * <http://www.doctrine-project.org>.
 */
namespace Doctrine\Common\Collections\Expr;


/**
 * An Expression visitor walks a graph of expressions and turns them into a
 * query for the underlying implementation.
 *
 * @author Benjamin Eberlei <kontakt@beberlei.de>
 */
abstract class ExpressionVisitor {

  /**
   * Convert a comparison expression into the target query language output
   *
   * @param Comparison $comparison
   *
   * @return mixed
   */
  public abstract function walkComparison(Comparison $comparison);

  /**
   * Convert a value expression into the target query language part.
   *
   * @param Value $value
   *
   * @return mixed
   */
  public abstract function walkValue(Value $value);

  /**
   * Convert a composite expression into the target query language output
   *
   * @param CompositeExpression $expr
   *
   * @return mixed
   */
  public abstract function walkCompositeExpression(CompositeExpression $expr);

  /**
   * Dispatch walking an expression to the appropriate handler.
   *
   * @param Expression
   *
   * @return mixed
   */
  public function dispatch(Expression $expr) {
    switch (true) {
      case $expr instanceof Comparison:
        return $this
          ->walkComparison($expr);
      case $expr instanceof Value:
        return $this
          ->walkValue($expr);
      case $expr instanceof CompositeExpression:
        return $this
          ->walkCompositeExpression($expr);
      default:
        throw new \RuntimeException("Unknown Expression " . get_class($expr));
    }
  }

}