| 1 | /* |
| 2 | * Copyright (c) 2023 Philippe Proulx <pproulx@efficios.com> |
| 3 | * |
| 4 | * SPDX-License-Identifier: MIT |
| 5 | */ |
| 6 | |
| 7 | #ifndef BABELTRACE_CPP_COMMON_BT2_OPTIONAL_BORROWED_OBJECT_HPP |
| 8 | #define BABELTRACE_CPP_COMMON_BT2_OPTIONAL_BORROWED_OBJECT_HPP |
| 9 | |
| 10 | #include <type_traits> |
| 11 | |
| 12 | #include "borrowed-object-proxy.hpp" |
| 13 | |
| 14 | namespace bt2 { |
| 15 | |
| 16 | /* |
| 17 | * An instance of this class template manages an optional contained |
| 18 | * borrowed object of type `ObjT`, that is, a borrowed object that may |
| 19 | * or may not be present. |
| 20 | * |
| 21 | * Such an object considers that a `nullptr` libbabeltrace2 object |
| 22 | * pointer means none. Therefore, using an `OptionalBorrowedObject` |
| 23 | * isn't more costly, in time and space, as using a libbabeltrace2 |
| 24 | * object pointer in C, but offers the typical C++ optional interface. |
| 25 | * |
| 26 | * There's no `bt2s::nullopt` equivalent: just use the default |
| 27 | * constructor or call reset(). |
| 28 | * |
| 29 | * There are a constructors an assignment operators which accept an |
| 30 | * instance of another wrapper object or of another optional borrowed |
| 31 | * object. For those, static assertions make sure that the assignment |
| 32 | * would work with borrowed objects, for example: |
| 33 | * |
| 34 | * auto sharedIntVal = createValue(23L); |
| 35 | * |
| 36 | * OptionalBorrowedObject<Value> myVal {*sharedIntVal}; |
| 37 | * |
| 38 | * This is needed because `OptionalBorrowedObject` only keeps a |
| 39 | * libbabeltrace2 pointer (`_mLibObjPtr`), therefore it doesn't |
| 40 | * automatically know the relation between wrapper classes. |
| 41 | */ |
| 42 | template <typename ObjT> |
| 43 | class OptionalBorrowedObject final |
| 44 | { |
| 45 | public: |
| 46 | using Obj = ObjT; |
| 47 | using LibObjPtr = typename ObjT::LibObjPtr; |
| 48 | |
| 49 | /* |
| 50 | * Builds an optional borrowed object without an object. |
| 51 | * |
| 52 | * Intentionally not explicit. |
| 53 | */ |
| 54 | OptionalBorrowedObject() noexcept = default; |
| 55 | |
| 56 | /* |
| 57 | * Builds an optional borrowed object with an instance of `ObjT` |
| 58 | * wrapping the libbabeltrace2 pointer `libObjPtr`. |
| 59 | * |
| 60 | * Intentionally not explicit. |
| 61 | */ |
| 62 | OptionalBorrowedObject(const LibObjPtr libObjPtr) noexcept : _mLibObjPtr {libObjPtr} |
| 63 | { |
| 64 | } |
| 65 | |
| 66 | /* |
| 67 | * Builds an optional borrowed object with an instance of `ObjT` |
| 68 | * constructed from `obj`. |
| 69 | * |
| 70 | * It must be possible to construct an instance of `ObjT` with an |
| 71 | * instance of `OtherObjT`. |
| 72 | * |
| 73 | * Intentionally not explicit. |
| 74 | */ |
| 75 | template <typename OtherObjT> |
| 76 | OptionalBorrowedObject(const OtherObjT obj) noexcept : _mLibObjPtr {obj.libObjPtr()} |
| 77 | { |
| 78 | static_assert(std::is_constructible<ObjT, OtherObjT>::value, |
| 79 | "`ObjT` is constructible with an instance of `OtherObjT`."); |
| 80 | } |
| 81 | |
| 82 | /* |
| 83 | * Builds an optional borrowed object from `optObj`, with or without |
| 84 | * an object. |
| 85 | * |
| 86 | * It must be possible to construct an instance of `ObjT` with an |
| 87 | * instance of `OtherObjT`. |
| 88 | * |
| 89 | * Intentionally not explicit. |
| 90 | */ |
| 91 | template <typename OtherObjT> |
| 92 | OptionalBorrowedObject(const OptionalBorrowedObject<OtherObjT> optObj) noexcept : |
| 93 | _mLibObjPtr {optObj.libObjPtr()} |
| 94 | { |
| 95 | static_assert(std::is_constructible<ObjT, OtherObjT>::value, |
| 96 | "`ObjT` is constructible with an instance of `OtherObjT`."); |
| 97 | } |
| 98 | |
| 99 | /* |
| 100 | * Makes this optional borrowed object have an instance of `ObjT` |
| 101 | * wrapping the libbabeltrace2 pointer `libObjPtr`. |
| 102 | */ |
| 103 | OptionalBorrowedObject& operator=(const LibObjPtr libObjPtr) noexcept |
| 104 | { |
| 105 | _mLibObjPtr = libObjPtr; |
| 106 | return *this; |
| 107 | } |
| 108 | |
| 109 | /* |
| 110 | * Makes this optional borrowed object have an instance of `ObjT` |
| 111 | * constructed from `obj`. |
| 112 | * |
| 113 | * It must be possible to construct an instance of `ObjT` with an |
| 114 | * instance of `OtherObjT`. |
| 115 | */ |
| 116 | template <typename OtherObjT> |
| 117 | OptionalBorrowedObject& operator=(const ObjT obj) noexcept |
| 118 | { |
| 119 | static_assert(std::is_constructible<ObjT, OtherObjT>::value, |
| 120 | "`ObjT` is constructible with an instance of `OtherObjT`."); |
| 121 | _mLibObjPtr = obj.libObjPtr(); |
| 122 | return *this; |
| 123 | } |
| 124 | |
| 125 | /* |
| 126 | * Sets this optional borrowed object to `optObj`. |
| 127 | * |
| 128 | * It must be possible to construct an instance of `ObjT` with an |
| 129 | * instance of `OtherObjT`. |
| 130 | */ |
| 131 | template <typename OtherObjT> |
| 132 | OptionalBorrowedObject& operator=(const OptionalBorrowedObject<ObjT> optObj) noexcept |
| 133 | { |
| 134 | static_assert(std::is_constructible<ObjT, OtherObjT>::value, |
| 135 | "`ObjT` is constructible with an instance of `OtherObjT`."); |
| 136 | _mLibObjPtr = optObj.libObjPtr(); |
| 137 | return *this; |
| 138 | } |
| 139 | |
| 140 | /* Wrapped libbabeltrace2 object pointer (may be `nullptr`) */ |
| 141 | LibObjPtr libObjPtr() const noexcept |
| 142 | { |
| 143 | return _mLibObjPtr; |
| 144 | } |
| 145 | |
| 146 | ObjT object() const noexcept |
| 147 | { |
| 148 | return ObjT {_mLibObjPtr}; |
| 149 | } |
| 150 | |
| 151 | ObjT operator*() const noexcept |
| 152 | { |
| 153 | return this->object(); |
| 154 | } |
| 155 | |
| 156 | /* |
| 157 | * We want to return the address of an `ObjT` instance here, but we |
| 158 | * only have a library pointer (`_mLibObjPtr`) because an `ObjT` |
| 159 | * instance may not wrap `nullptr`. |
| 160 | * |
| 161 | * Therefore, return a proxy object which holds an internal |
| 162 | * `ObjT` instance and implements operator->() itself. |
| 163 | * |
| 164 | * In other words, doing `myOptObj->something()` is equivalent to |
| 165 | * calling `myOptObj.operator->().operator->()->something()`. |
| 166 | */ |
| 167 | BorrowedObjectProxy<ObjT> operator->() const noexcept |
| 168 | { |
| 169 | return BorrowedObjectProxy<ObjT> {_mLibObjPtr}; |
| 170 | } |
| 171 | |
| 172 | bool hasObject() const noexcept |
| 173 | { |
| 174 | return _mLibObjPtr; |
| 175 | } |
| 176 | |
| 177 | explicit operator bool() const noexcept |
| 178 | { |
| 179 | return this->hasObject(); |
| 180 | } |
| 181 | |
| 182 | void reset() noexcept |
| 183 | { |
| 184 | _mLibObjPtr = nullptr; |
| 185 | } |
| 186 | |
| 187 | private: |
| 188 | typename ObjT::LibObjPtr _mLibObjPtr = nullptr; |
| 189 | }; |
| 190 | |
| 191 | } /* namespace bt2 */ |
| 192 | |
| 193 | #endif /* BABELTRACE_CPP_COMMON_BT2_OPTIONAL_BORROWED_OBJECT_HPP */ |