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/**
* Copyright (C) 2019-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <type_traits>
namespace mongo::tree_walker {
/**
* A template type which resolves to 'const T*' if 'IsConst' argument is 'true', and to 'T*'
* otherwise.
*/
template <bool IsConst, typename T>
using MaybeConstPtr = typename std::conditional<IsConst, const T*, T*>::type;
/**
* Provided with a Walker and a Node, walk() calls each of the following:
* * walker.preVisit() once before walking to each child.
* * walker.inVisit() between walking to each child. It is called multiple times, once between each
* pair of children. walker.inVisit() is skipped if the Node has fewer than two children.
* * walker.postVisit() once after walking to each child.
*
* Each of the Node's children is recursively walked and the same three methods are called for it.
*
* The Node type should either provide begin() and end() methods returning an iterator to walk its
* children, or define begin() and end() functions taking a Node reference which return the
* iterator.
*
* If the caller doesn't intend to modify the tree, then the template argument 'IsConst' should be
* set to 'true'. In this case the 'node' pointer will be qualified with 'const'.
*/
template <bool IsConst, typename Node, typename Walker>
void walk(MaybeConstPtr<IsConst, Node> node, Walker* walker) {
if (node) {
walker->preVisit(node);
auto count = 0ull;
for (auto&& child : *node) {
if (count) {
walker->inVisit(count, node);
}
++count;
walk<IsConst, Node, Walker>(&*child, walker);
}
walker->postVisit(node);
}
}
} // namespace mongo::tree_walker
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