select_lex_visitor.h

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#ifndef Query_block_VISITOR_INCLUDED
#define Query_block_VISITOR_INCLUDED
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/**
  @file select_lex_visitor.h
  Visitor interface for parse trees.
*/
 
class Query_expression;
class Query_block;
class Item;
 
/**
  Abstract base class for traversing the Query_block tree. In order to use it,
  a client defines a subclass, overriding the member functions that visit the
  objects of interest. If a function returns true, traversal is aborted.
*/
class Select_lex_visitor {
 public:
  virtual bool visits_in_prefix_order() const { return true; }
 
  bool visit(Query_expression *unit) { return visit_union(unit); }
  bool visit(Query_block *query_block) {
    return visit_query_block(query_block);
  }
 
  /// Called for all nodes of all expression trees (i.e. Item trees).
  bool visit(Item *item) { return visit_item(item); }
 
  virtual ~Select_lex_visitor() = 0;
 
 protected:
  virtual bool visit_union(Query_expression *) { return false; }
  virtual bool visit_query_block(Query_block *) { return false; }
  virtual bool visit_item(Item *) { return false; }
};
 
#endif  // Query_block_VISITOR_INCLUDED