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
99 lines
2.4 KiB
C++
99 lines
2.4 KiB
C++
/*
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* Copyright (C) 2015-present ScyllaDB
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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 <functional>
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#include <compare>
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#include "timestamp.hh"
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#include "gc_clock.hh"
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#include "utils/hashing.hh"
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/**
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* Represents deletion operation. Can be commuted with other tombstones via apply() method.
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* Can be empty.
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*/
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struct tombstone final {
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api::timestamp_type timestamp;
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gc_clock::time_point deletion_time;
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tombstone(api::timestamp_type timestamp, gc_clock::time_point deletion_time)
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: timestamp(timestamp)
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, deletion_time(deletion_time)
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{ }
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tombstone()
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: tombstone(api::missing_timestamp, {})
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{ }
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std::strong_ordering operator<=>(const tombstone& t) const = default;
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bool operator==(const tombstone&) const = default;
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explicit operator bool() const {
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return timestamp != api::missing_timestamp;
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}
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void apply(const tombstone& t) noexcept {
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if (*this < t) {
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*this = t;
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}
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}
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// See reversibly_mergeable.hh
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void apply_reversibly(tombstone& t) noexcept {
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std::swap(*this, t);
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apply(t);
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}
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// See reversibly_mergeable.hh
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void revert(tombstone& t) noexcept {
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std::swap(*this, t);
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}
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tombstone operator+(const tombstone& t) {
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auto result = *this;
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result.apply(t);
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return result;
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}
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};
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template <>
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struct fmt::formatter<tombstone> : fmt::formatter<std::string_view> {
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template <typename FormatContext>
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auto format(const tombstone& t, FormatContext& ctx) const {
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if (t) {
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return fmt::format_to(ctx.out(),
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"{{tombstone: timestamp={}, deletion_time={}}}",
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t.timestamp, t.deletion_time.time_since_epoch().count());
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} else {
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return fmt::format_to(ctx.out(),
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"{{tombstone: none}}");
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}
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}
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};
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static inline std::ostream& operator<<(std::ostream& out, const tombstone& t) {
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fmt::print(out, "{}", t);
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return out;
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}
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template<>
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struct appending_hash<tombstone> {
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template<typename Hasher>
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void operator()(Hasher& h, const tombstone& t) const {
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feed_hash(h, t.timestamp);
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feed_hash(h, t.deletion_time);
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}
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};
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// Determines whether tombstone may be GC-ed.
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using can_gc_fn = std::function<bool(tombstone)>;
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extern can_gc_fn always_gc;
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