+/* 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
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