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20 namespace Doctrine\Common\Collections\Expr;
23 * An Expression visitor walks a graph of expressions and turns them into a
24 * query for the underlying implementation.
26 * @author Benjamin Eberlei <kontakt@beberlei.de>
28 abstract class ExpressionVisitor
31 * Convert a comparison expression into the target query language output
33 * @param Comparison $comparison
37 abstract public function walkComparison(Comparison $comparison);
40 * Convert a value expression into the target query language part.
46 abstract public function walkValue(Value $value);
49 * Convert a composite expression into the target query language output
51 * @param CompositeExpression $expr
55 abstract public function walkCompositeExpression(CompositeExpression $expr);
58 * Dispatch walking an expression to the appropriate handler.
64 public function dispatch(Expression $expr)
67 case ($expr instanceof Comparison):
68 return $this->walkComparison($expr);
70 case ($expr instanceof Value):
71 return $this->walkValue($expr);
73 case ($expr instanceof CompositeExpression):
74 return $this->walkCompositeExpression($expr);
77 throw new \RuntimeException("Unknown Expression " . get_class($expr));