text: /* Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
   * Use of this file is governed by the BSD 3-clause license that
   * can be found in the LICENSE.txt file in the project root.
   */
  
  #pragma once
  
  #include "tree/ParseTreeVisitor.h"
  
  namespace antlr4 {
  namespace tree {
  
    class ANTLR4CPP_PUBLIC AbstractParseTreeVisitor : public ParseTreeVisitor {
    public:
      /// The default implementation calls <seealso cref="ParseTree#accept"/> on the
      /// specified tree.
      virtual antlrcpp::Any visit(ParseTree *tree) override {
        return tree->accept(this);
      }
  
      /**
       * <p>The default implementation initializes the aggregate result to
       * {@link #defaultResult defaultResult()}. Before visiting each child, it
       * calls {@link #shouldVisitNextChild shouldVisitNextChild}; if the result
       * is {@code false} no more children are visited and the current aggregate
       * result is returned. After visiting a child, the aggregate result is
       * updated by calling {@link #aggregateResult aggregateResult} with the
       * previous aggregate result and the result of visiting the child.</p>
       *
       * <p>The default implementation is not safe for use in visitors that modify
       * the tree structure. Visitors that modify the tree should override this
       * method to behave properly in respect to the specific algorithm in use.</p>
       */
      virtual antlrcpp::Any visitChildren(ParseTree *node) override {
        antlrcpp::Any result = defaultResult();
        size_t n = node->children.size();
        for (size_t i = 0; i < n; i++) {
          if (!shouldVisitNextChild(node, result)) {
            break;
          }
  
          antlrcpp::Any childResult = node->children[i]->accept(this);
          result = aggregateResult(result, childResult);
        }
  
        return result;
      }
  
      /// The default implementation returns the result of
      /// <seealso cref="#defaultResult defaultResult"/>.
      virtual antlrcpp::Any visitTerminal(TerminalNode * /*node*/) override {
        return defaultResult();
      }
  
      /// The default implementation returns the result of
      /// <seealso cref="#defaultResult defaultResult"/>.
      virtual antlrcpp::Any visitErrorNode(ErrorNode * /*node*/) override {
        return defaultResult();
      }
  
    protected:
      /// <summary>
      /// Gets the default value returned by visitor methods. This value is
      /// returned by the default implementations of
      /// <seealso cref="#visitTerminal visitTerminal"/>, <seealso cref="#visitErrorNode visitErrorNode"/>.
      /// The default implementation of <seealso cref="#visitChildren visitChildren"/>
      /// initializes its aggregate result to this value.
      /// <p/>
      /// The base implementation returns {@code null}.
      /// </summary>
      /// <returns> The default value returned by visitor methods. </returns>
      virtual antlrcpp::Any defaultResult() {
        return nullptr; // support isNotNull
      }
  
      /// <summary>
      /// Aggregates the results of visiting multiple children of a node. After
      /// either all children are visited or <seealso cref="#shouldVisitNextChild"/> returns
      /// {@code false}, the aggregate value is returned as the result of
      /// <seealso cref="#visitChildren"/>.
      /// <p/>
      /// The default implementation returns {@code nextResult}, meaning
      /// <seealso cref="#visitChildren"/> will return the result of the last child visited
      /// (or return the initial value if the node has no children).
      /// </summary>
      /// <param name="aggregate"> The previous aggregate value. In the default
      /// implementation, the aggregate value is initialized to
      /// <seealso cref="#defaultResult"/>, which is passed as the {@code aggregate} argument
      /// to this method after the first child node is visited. </param>
      /// <param name="nextResult"> The result of the immediately preceeding call to visit
      /// a child node.
      /// </param>
      /// <returns> The updated aggregate result. </returns>
      virtual antlrcpp::Any aggregateResult(antlrcpp::Any /*aggregate*/, const antlrcpp::Any &nextResult) {
        return nextResult;
      }
  
      /// <summary>
      /// This method is called after visiting each child in
      /// <seealso cref="#visitChildren"/>. This method is first called before the first
      /// child is visited; at that point {@code currentResult} will be the initial
      /// value (in the default implementation, the initial value is returned by a
      /// call to <seealso cref="#defaultResult"/>. This method is not called after the last
      /// child is visited.
      /// <p/>
      /// The default implementation always returns {@code true}, indicating that
      /// {@code visitChildren} should only return after all children are visited.
      /// One reason to override this method is to provide a "short circuit"
      /// evaluation option for situations where the result of visiting a single
      /// child has the potential to determine the result of the visit operation as
      /// a whole.
      /// </summary>
      /// <param name="node"> The <seealso cref="ParseTree"/> whose children are currently being
      /// visited. </param>
      /// <param name="currentResult"> The current aggregate result of the children visited
      /// to the current point.
      /// </param>
      /// <returns> {@code true} to continue visiting children. Otherwise return
      /// {@code false} to stop visiting children and immediately return the
      /// current aggregate result from <seealso cref="#visitChildren"/>. </returns>
      virtual bool shouldVisitNextChild(ParseTree * /*node*/, const antlrcpp::Any &/*currentResult*/) {
        return true;
      }
  
    };
  
  } // namespace tree
  } // namespace antlr4
  