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<?php
namespace Doctrine\Common\Collections\Expr;
use RuntimeException;
use function get_class;
/**
* An Expression visitor walks a graph of expressions and turns them into a
* query for the underlying implementation.
*/
abstract class ExpressionVisitor
{
/**
* Converts a comparison expression into the target query language output.
*
* @return mixed
*/
abstract public function walkComparison(Comparison $comparison);
/**
* Converts a value expression into the target query language part.
*
* @return mixed
*/
abstract public function walkValue(Value $value);
/**
* Converts a composite expression into the target query language output.
*
* @return mixed
*/
abstract public function walkCompositeExpression(CompositeExpression $expr);
/**
* Dispatches walking an expression to the appropriate handler.
*
* @return mixed
*
* @throws RuntimeException
*/
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));
}
}
}
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