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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
41 lines
1.5 KiB
C++
41 lines
1.5 KiB
C++
/*
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* Copyright (C) 2019-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 "dht/i_partitioner.hh"
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// Wraps ring_position or ring_position_view so either is compatible with old-style C++: default
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// constructor, stateless comparators, yada yada.
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// The motivations for supporting both types are to make containers self-sufficient by not relying
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// on callers to keep ring position alive, allow lookup on containers that don't support different
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// key types, and also avoiding unnecessary copies.
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class compatible_ring_position_or_view {
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schema_ptr _schema;
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lw_shared_ptr<dht::ring_position> _rp;
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dht::ring_position_view_opt _rpv; // optional only for default ctor, nothing more
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public:
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compatible_ring_position_or_view() = default;
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explicit compatible_ring_position_or_view(schema_ptr s, dht::ring_position rp)
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: _schema(std::move(s)), _rp(make_lw_shared<dht::ring_position>(std::move(rp))), _rpv(dht::ring_position_view(*_rp)) {
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}
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explicit compatible_ring_position_or_view(const schema& s, dht::ring_position_view rpv)
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: _schema(s.shared_from_this()), _rpv(rpv) {
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}
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const dht::ring_position_view& position() const {
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return *_rpv;
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}
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std::strong_ordering operator<=>(const compatible_ring_position_or_view& other) const {
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return dht::ring_position_tri_compare(*_schema, position(), other.position());
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}
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bool operator==(const compatible_ring_position_or_view& other) const {
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return *this <=> other == 0;
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}
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};
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