/* Copyright 2019-2020 David Robillard Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies. THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */ #ifndef SERD_DETAIL_OPTIONAL_HPP #define SERD_DETAIL_OPTIONAL_HPP #include #include #include namespace serd { namespace detail { struct ConstructNullOptional { }; /** A simple optional wrapper around a wrapped type with a pointer-like API This works like a typical optional type, but only works with Wrapper types, and exploits the fact that these are interally just pointers to avoid adding space overhead for an "is_set" flag, like a generic optional class would. Types must explicitly opt-in to being optional by providing a constructor that takes a single ContructNullOptional argument. This constructor should only be used by the Optional implementation, which guarantees that such an object will not be used except by calling its cobj() method. */ template class Optional { public: using CType = typename T::CType; Optional() : _value(nullptr) {} // NOLINTNEXTLINE(hicpp-explicit-conversions, modernize-pass-by-value) Optional(const T& value) : _value(value) {} // NOLINTNEXTLINE(hicpp-explicit-conversions) Optional(T&& value) : _value(std::move(value)) {} template ::value>::type> // NOLINTNEXTLINE(hicpp-explicit-conversions) Optional(U&& value) : _value(std::forward(value)) { } void reset() { _value = T{nullptr}; } const T& operator*() const { assert(_value.cobj()); return _value; } T& operator*() { assert(_value.cobj()); return _value; } const T* operator->() const { assert(_value.cobj()); return &_value; } T* operator->() { assert(_value.cobj()); return &_value; } bool operator==(const Optional& optional) { return (!*this && !optional) || (*this && optional && _value == optional._value); } bool operator!=(const Optional& optional) { return !operator==(optional); } explicit operator bool() const { return _value.cobj(); } bool operator!() const { return !_value.cobj(); } inline CType* cobj() { return _value.cobj(); } inline const CType* cobj() const { return _value.cobj(); } private: T _value; }; } // namespace detail template constexpr detail::Optional make_optional(T&& value) { return detail::Optional{std::forward(value)}; } template constexpr detail::Optional make_optional(Args&&... args) { return detail::Optional{std::forward(args)...}; } } // namespace serd #endif // SERD_DETAIL_OPTIONAL_HPP