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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <functional>
namespace vespalib {
struct visit_ranges_either {};
struct visit_ranges_first : visit_ranges_either {};
struct visit_ranges_second : visit_ranges_either {};
struct visit_ranges_both {};
/**
* Visit elements from two distinct ranges in the order defined by the
* given comparator. The comparator must define a strict-weak ordering
* across all elements from both ranges and each range must already be
* sorted according to the comparator before calling this
* function. Pairs of elements from the two ranges (one from each)
* that are equal according to the comparator will be visited by a
* single callback. The different cases ('from the first range', 'from
* the second range' and 'from both ranges') are indicated by using
* tagged dispatch in the visitation callback.
*
* An example treating both inputs equally:
* <pre>
* TEST(VisitRangeExample, set_intersection) {
* std::vector<int> first({1,3,7});
* std::vector<int> second({2,3,8});
* std::vector<int> result;
* vespalib::visit_ranges(overload{[](visit_ranges_either, int) {},
* [&result](visit_ranges_both, int x, int) { result.push_back(x); }},
* first.begin(), first.end(), second.begin(), second.end());
* EXPECT_EQ(result, std::vector<int>({3}));
* }
* </pre>
*
* An example treating the inputs differently:
* <pre>
* TEST(VisitRangeExample, set_subtraction) {
* std::vector<int> first({1,3,7});
* std::vector<int> second({2,3,8});
* std::vector<int> result;
* vespalib::visit_ranges(overload{[&result](visit_ranges_first, int a) { result.push_back(a); },
* [](visit_ranges_second, int) {},
* [](visit_ranges_both, int, int) {}},
* first.begin(), first.end(), second.begin(), second.end());
* EXPECT_EQ(result, std::vector<int>({1,7}));
* }
* </pre>
*
* The intention of this function is to simplify the implementation of
* merge-like operations.
**/
template <typename V, typename ItA, typename ItB, typename Cmp = std::less<> >
void visit_ranges(V &&visitor, ItA pos_a, ItA end_a, ItB pos_b, ItB end_b, Cmp cmp = Cmp()) {
while ((pos_a != end_a) && (pos_b != end_b)) {
if (cmp(*pos_a, *pos_b)) {
visitor(visit_ranges_first(), *pos_a);
++pos_a;
} else if (cmp(*pos_b, *pos_a)) {
visitor(visit_ranges_second(), *pos_b);
++pos_b;
} else {
visitor(visit_ranges_both(), *pos_a, *pos_b);
++pos_a;
++pos_b;
}
}
while (pos_a != end_a) {
visitor(visit_ranges_first(), *pos_a);
++pos_a;
}
while (pos_b != end_b) {
visitor(visit_ranges_second(), *pos_b);
++pos_b;
}
}
}
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