f5b05cf981
in C++20, compiler generate operator!=() if the corresponding operator==() is already defined, the language now understands that the comparison is symmetric in the new standard. fortunately, our operator!=() is always equivalent to `! operator==()`, this matches the behavior of the default generated operator!=(). so, in this change, all `operator!=` are removed. in addition to the defaulted operator!=, C++20 also brings to us the defaulted operator==() -- it is able to generated the operator==() if the member-wise lexicographical comparison. under some circumstances, this is exactly what we need. so, in this change, if the operator==() is also implemented as a lexicographical comparison of all memeber variables of the class/struct in question, it is implemented using the default generated one by removing its body and mark the function as `default`. moreover, if the class happen to have other comparison operators which are implemented using lexicographical comparison, the default generated `operator<=>` is used in place of the defaulted `operator==`. sometimes, we fail to mark the operator== with the `const` specifier, in this change, to fulfil the need of C++ standard, and to be more correct, the `const` specifier is added. also, to generate the defaulted operator==, the operand should be `const class_name&`, but it is not always the case, in the class of `version`, we use `version` as the parameter type, to fulfill the need of the C++ standard, the parameter type is changed to `const version&` instead. this does not change the semantic of the comparison operator. and is a more idiomatic way to pass non-trivial struct as function parameters. please note, because in C++20, both operator= and operator<=> are symmetric, some of the operators in `multiprecision` are removed. they are the symmetric form of the another variant. if they were not removed, compiler would, for instance, find ambiguous overloaded operator '=='. this change is a cleanup to modernize the code base with C++20 features. Signed-off-by: Kefu Chai <kefu.chai@scylladb.com> Closes #13687
104 lines
2.9 KiB
C++
104 lines
2.9 KiB
C++
/*
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* Copyright (C) 2015-present ScyllaDB
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*
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*/
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/*
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* SPDX-License-Identifier: AGPL-3.0-or-later
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*/
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#pragma once
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#include <vector>
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#include <sys/types.h>
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// Single-pass range over cartesian product of vectors.
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// Note:
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// {a, b, c} x {1, 2} = {{a, 1}, {a, 2}, {b, 1}, {b, 2}, {c, 1}, {c, 2}}
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template<typename T>
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struct cartesian_product {
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const std::vector<std::vector<T>>& _vec_of_vecs;
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public:
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class iterator {
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public:
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using iterator_category = std::forward_iterator_tag;
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using value_type = std::vector<T>;
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using difference_type = std::ptrdiff_t;
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using pointer = std::vector<T>*;
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using reference = std::vector<T>&;
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private:
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size_t _pos;
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const std::vector<std::vector<T>>* _vec_of_vecs;
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value_type _current;
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std::vector<typename std::vector<T>::const_iterator> _iterators;
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public:
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struct end_tag {};
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iterator(end_tag) : _pos(-1) {}
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iterator(const std::vector<std::vector<T>>& vec_of_vecs) : _pos(0), _vec_of_vecs(&vec_of_vecs) {
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_iterators.reserve(vec_of_vecs.size());
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for (auto&& vec : vec_of_vecs) {
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_iterators.push_back(vec.begin());
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if (vec.empty()) {
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_pos = -1;
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break;
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}
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}
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}
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value_type& operator*() {
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_current.clear();
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_current.reserve(_vec_of_vecs->size());
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for (auto& i : _iterators) {
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_current.emplace_back(*i);
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}
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return _current;
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}
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void operator++() {
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++_pos;
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for (ssize_t i = _iterators.size() - 1; i >= 0; --i) {
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++_iterators[i];
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if (_iterators[i] != (*_vec_of_vecs)[i].end()) {
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return;
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}
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_iterators[i] = (*_vec_of_vecs)[i].begin();
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}
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// If we're here it means we've covered every combination
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_pos = -1;
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}
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bool operator==(const iterator& o) const { return _pos == o._pos; }
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};
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public:
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cartesian_product(const std::vector<std::vector<T>>& vec_of_vecs) : _vec_of_vecs(vec_of_vecs) {}
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iterator begin() { return iterator(_vec_of_vecs); }
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iterator end() { return iterator(typename iterator::end_tag()); }
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};
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template<typename T>
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static inline
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size_t cartesian_product_size(const std::vector<std::vector<T>>& vec_of_vecs) {
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size_t r = 1;
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for (auto&& vec : vec_of_vecs) {
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r *= vec.size();
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}
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return r;
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}
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template<typename T>
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static inline
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bool cartesian_product_is_empty(const std::vector<std::vector<T>>& vec_of_vecs) {
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for (auto&& vec : vec_of_vecs) {
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if (vec.empty()) {
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return true;
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}
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}
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return vec_of_vecs.empty();
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}
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template<typename T>
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static inline
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cartesian_product<T> make_cartesian_product(const std::vector<std::vector<T>>& vec_of_vecs) {
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return cartesian_product<T>(vec_of_vecs);
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}
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