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ce7bd9f595
This change makes minor improvements to the optional class used with pre-C++17 compilers. - adds operator== and operator!= - adds various missing noexcept (but not constexpr) decorations - defines operator bool in terms of has_value Note that some constexpr decorations would require C++17 anyway. * include/abg-cxx-compat.h (optional): Add operator== and operator!=. Add noexcept decorations. Tweak operator bool. Reviewed-by: Matthias Maennich <maennich@google.com> Signed-off-by: Giuliano Procida <gprocida@google.com>
118 lines
2.1 KiB
C++
118 lines
2.1 KiB
C++
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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// -*- Mode: C++ -*-
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//
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// Copyright (C) 2019-2022 Google, Inc.
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/// @file
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#ifndef __ABG_CXX_COMPAT_H
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#define __ABG_CXX_COMPAT_H
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// C++17 support (via custom implementations if compiled with earlier standard)
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#if __cplusplus >= 201703L
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#include <optional>
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#else
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#include <stdexcept> // for throwing std::runtime_error("bad_optional_access")
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#endif
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namespace abg_compat {
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#if __cplusplus >= 201703L
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using std::optional;
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#else
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// <optional>
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/// Simplified implementation of std::optional just enough to be used as a
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/// replacement for our purposes and when compiling with pre C++17.
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///
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/// The implementation intentionally does not support a whole lot of features
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/// to minimize the maintenance effort with this.
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template <typename T> class optional
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{
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bool has_value_;
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T value_;
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public:
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optional() : has_value_(false), value_() {}
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optional(const T& value) : has_value_(true), value_(value) {}
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bool
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has_value() const noexcept
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{
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return has_value_;
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}
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const T&
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value() const
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{
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if (!has_value_)
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throw std::runtime_error("bad_optional_access");
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return value_;
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}
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const T
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value_or(const T& default_value) const
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{
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if (!has_value_)
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return default_value;
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return value_;
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}
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const T&
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operator*() const& noexcept
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{ return value_; }
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T&
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operator*() & noexcept
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{ return value_; }
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const T*
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operator->() const noexcept
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{ return &value_; }
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T*
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operator->() noexcept
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{ return &value_; }
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optional&
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operator=(const T& value)
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{
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has_value_ = true;
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value_ = value;
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return *this;
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}
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explicit operator bool() const noexcept { return has_value(); }
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};
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template <typename T, typename U>
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bool
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operator==(const optional<T>& lhs, const optional<U>& rhs)
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{
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if (!lhs.has_value() && !rhs.has_value())
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return true;
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if (!lhs.has_value() || !rhs.has_value())
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return false;
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return lhs.value() == rhs.value();
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}
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template <typename T, typename U>
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bool
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operator!=(const optional<T>& lhs, const optional<U>& rhs)
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{
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return !(lhs == rhs);
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}
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#endif
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}
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#endif // __ABG_CXX_COMPAT_H
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