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14 <div class="titlepage"><div><div><h1 style="clear: both"><code>basic_result<T, E, NoValuePolicy></code></h1></div></div></div>
15 <div class="toc"><dl class="toc">
20 <dt><a href="#design-rationale">Design rationale</a></dt>
21 <dt><a href="#public-member-type-aliases">Public member type aliases</a></dt>
22 <dt><a href="#protected-member-predicate-booleans">Protected member predicate booleans</a>
24 <dt><a href="#summary-of-standard-requirements-provided-https-en-cppreference-com-w-cpp-named-req">Summary of <a href="https://en.cppreference.com/w/cpp/named_req">standard requirements provided</a></a></dt>
26 <dt><a href="#public-member-functions">Public member functions</a>
28 <dt><a href="#disabling-constructors">Disabling constructors</a></dt>
36 <p>A sum type carrying either a <code>T</code> or an <code>E</code>, with <code>NoValuePolicy</code> specifying what to do if one tries to read state which isn’t there. Either or both of <code>T</code> and <code>E</code> can be <code>void</code> to indicate no value for that state is present. Note that <code>E = void</code> makes basic result into effectively an <code>optional<T></code>, but with <code>NoValuePolicy</code> configurable behaviour. Detectable using <a href="../../reference/traits/is_basic_result.html" class="api-reference"><code>is_basic_result<T></code></a>
39 <p><em>Requires</em>: Concept requirements if C++ 20, else static asserted:</p>
42 <li>That trait <a href="../../reference/traits/type_can_be_used_in_basic_result.html" class="api-reference"><code>type_can_be_used_in_basic_result<R></code></a>
43 is true for both <code>T</code> and <code>E</code>.</li>
44 <li>That either <code>E</code> is <code>void</code> or <code>DefaultConstructible</code>.</li>
47 <p><em>Namespace</em>: <code>BOOST_OUTCOME_V2_NAMESPACE</code></p>
49 <p><em>Header</em>: <code><boost/outcome/basic_result.hpp></code></p>
51 <p><em>Inclusions</em>: The very lightest weight of C and C++ header files:</p>
54 <li><code><cstdint></code></li>
55 <li><code><initializer_list></code></li>
56 <li><code><iosfwd></code></li>
57 <li><code><new></code></li>
58 <li><code><type_traits></code></li>
59 <li>If <a href="../../reference/macros/in_place_type.html" class="api-reference"><code>BOOST_OUTCOME_USE_STD_IN_PLACE_TYPE</code></a>
60 is <code>1</code>, <code><utility></code> (defaults to <code>1</code> for C++ 17 or later only)</li>
61 <li>If C++ exceptions disabled and <code>BOOST_OUTCOME_DISABLE_EXECINFO</code> undefined only (used to print stack backtraces on “exception throw”):
64 <li><code><sal.h></code> (Windows only)</li>
65 <li><code><stddef.h></code> (Windows only)</li>
66 <li><code><string.h></code> (Windows only)</li>
67 <li><code><execinfo.h></code> (POSIX only)</li>
69 <li><code><cstdio></code></li>
70 <li><code><cstdlib></code></li>
71 <li><code><cassert></code></li>
74 <p>This very light weight set of inclusion dependencies makes basic result suitable for use in global header files of very large C++ codebases.</p>
76 <h3 id="design-rationale">Design rationale</h3>
78 <p>The basic result type is the main workhorse type of the Outcome library, providing a simple sum type with optional values representing success or disappointment. Unlike
79 <a href="https://wg21.link/P0323" class="api-reference" target="_blank"><i class="fa fa-book" aria-hidden="true"></i> P0323 <code>std::expected<T, E></code></a>
80 , Outcome’s result type is designed specifically for convenience when implementing failure handling across very large codebases, and it has a number of API differences to facilitate that.</p>
82 <p>The first major design difference is that basic result models its constructor design on
83 <a href="https://en.cppreference.com/w/cpp/utility/variant" class="api-reference" target="_blank"><i class="fa fa-book" aria-hidden="true"></i> <code>std::variant<...></code></a>
84 , rather than modelling
85 <a href="https://en.cppreference.com/w/cpp/utility/optional" class="api-reference" target="_blank"><i class="fa fa-book" aria-hidden="true"></i> <code>std::optional<T></code></a>
86 ’s constructor design like <code>std::expected<T, E></code> does. This means that basic result will implicitly construct either a <code>T</code> or an <code>E</code> if doing so is unambiguous, same as <code>variant</code> does. Where implicit construction is ambiguous, the implicit constructors disable and a <code>T</code> or <code>E</code> can be specified via <a href="../../reference/types/in_place_type_t.html" class="api-reference"><code>in_place_type_t<T></code></a>
87 , or via <a href="../../reference/types/success_type.html" class="api-reference"><code>success_type<T></code></a>
88 or <a href="../../reference/traits/is_failure_type.html" class="api-reference"><code>failure_type<T></code></a>
89 . We implement a subset of variant’s constructors for improved compile time impact, so the implicit and explicit constructor design is split into fixed subsets to reduce SFINAE execution.</p>
91 <p>The second major design difference is that union storage is NOT used, as it is assumed that <code>sizeof(E)</code> will be small for failure handling. This very considerably reduces load on the compiler, and substantially improves compile times in very large C++ 14 codebases, because copies and moves do not need to jump through complex ceremony in order to implement the never-empty guarantees which would be required in a union storage based implementation (C++ 17 onwards does far fewer copy and move constructor instantiations, but it all adds up – work avoided is always the fastest).</p>
93 <h3 id="public-member-type-aliases">Public member type aliases</h3>
96 <li><code>value_type</code> is <code>T</code>.</li>
97 <li><code>error_type</code> is <code>E</code>.</li>
98 <li><code>value_type_if_enabled</code> is <code>T</code> if construction from <code>T</code> is available, else it is a usefully named unusable internal type.</li>
99 <li><code>error_type_if_enabled</code> is <code>E</code> if construction from <code>E</code> is available, else it is a usefully named unusable internal type.</li>
100 <li><code>rebind<A, B = E, C = NoValuePolicy></code> is <code>basic_result<A, B, C></code>.</li>
103 <h3 id="protected-member-predicate-booleans">Protected member predicate booleans</h3>
106 <li><p><code>predicate::constructors_enabled</code> is constexpr boolean true if decayed <code>value_type</code> and decayed <code>error_type</code> are not the same type.</p></li>
108 <li><p><code>predicate::implicit_constructors_enabled</code> is constexpr boolean true if:</p>
111 <li><code>predicate::constructors_enabled</code> is true.</li>
112 <li>Trait <a href="../../reference/traits/is_error_type.html" class="api-reference"><code>is_error_type<E></code></a>
113 is not true for both decayed <code>value_type</code> and decayed <code>error_type</code> at the same time.</li>
114 <li><code>value_type</code> is not implicitly constructible from <code>error_type</code> and <code>error_type</code> is not implicitly constructible from <code>value_type</code>.<br>OR<br>trait <a href="../../reference/traits/is_error_type.html" class="api-reference"><code>is_error_type<E></code></a>
115 is true for decayed <code>error_type</code> and <code>error_type</code> is not implicitly constructible from <code>value_type</code> and <code>value_type</code> is an integral type.</li>
118 <li><p><code>predicate::enable_value_converting_constructor<A></code> is constexpr boolean true if:</p>
121 <li><code>predicate::constructors_enabled</code> is true.</li>
122 <li>Decayed <code>A</code> is not this <code>basic_result</code> type.</li>
123 <li><code>predicate::implicit_constructors_enabled</code> is true.</li>
124 <li>Decayed <code>A</code> is not an <code>in_place_type_t</code>.</li>
125 <li>Trait <a href="../../reference/traits/is_error_type_enum.html" class="api-reference"><code>is_error_type_enum<E, Enum></code></a>
126 is false for <code>error_type</code> and decayed <code>A</code>.</li>
127 <li><code>value_type</code> is implicitly constructible from <code>A</code> and <code>error_type</code> is not implicitly constructible from <code>A</code>.<br>OR<br><code>value_type</code> is the exact same type as decayed <code>A</code> and <code>value_type</code> is implicitly constructible from <code>A</code>.</li>
130 <li><p><code>predicate::enable_error_converting_constructor<A></code> is constexpr boolean true if:</p>
133 <li><code>predicate::constructors_enabled</code> is true.</li>
134 <li>Decayed <code>A</code> is not this <code>basic_result</code> type.</li>
135 <li><code>predicate::implicit_constructors_enabled</code> is true.</li>
136 <li>Decayed <code>A</code> is not an <code>in_place_type_t</code>.</li>
137 <li>Trait <a href="../../reference/traits/is_error_type_enum.html" class="api-reference"><code>is_error_type_enum<E, Enum></code></a>
138 is false for <code>error_type</code> and decayed <code>A</code>.</li>
139 <li><code>value_type</code> is not implicitly constructible from <code>A</code> and <code>error_type</code> is implicitly constructible from <code>A</code>.<br>OR<br><code>error_type</code> is the exact same type as decayed <code>A</code> and <code>error_type</code> is implicitly constructible from <code>A</code>.</li>
142 <li><p><code>predicate::enable_error_condition_converting_constructor<ErrorCondEnum></code> is constexpr boolean true if:</p>
145 <li><code>predicate::constructors_enabled</code> is true.</li>
146 <li>Decayed <code>ErrorCondEnum</code> is not this <code>basic_result</code> type.</li>
147 <li>Decayed <code>ErrorCondEnum</code> is not an <code>in_place_type_t</code>.</li>
148 <li>Trait <a href="../../reference/traits/is_error_type_enum.html" class="api-reference"><code>is_error_type_enum<E, Enum></code></a>
149 is true for <code>error_type</code> and decayed <code>ErrorCondEnum</code>.</li>
152 <li><p><code>predicate::enable_compatible_conversion<A, B, C></code> is constexpr boolean true if:</p>
155 <li><code>predicate::constructors_enabled</code> is true.</li>
156 <li><code>basic_result<A, B, C></code> is not this <code>basic_result</code> type.</li>
157 <li><code>A</code> is <code>void</code> OR <code>value_type</code> is explicitly constructible from <code>A</code>.</li>
158 <li><code>B</code> is <code>void</code> OR <code>error_type</code> is explicitly constructible from <code>B</code>.</li>
161 <li><p><code>predicate::enable_make_error_code_compatible_conversion<A, B, C></code> is constexpr boolean true if:</p>
164 <li><code>predicate::constructors_enabled</code> is true.</li>
165 <li><code>basic_result<A, B, C></code> is not this <code>basic_result</code> type.</li>
166 <li>Trait "/home/travis/build/ned14/boost-outcome/doc/src/content/reference/types/basic_result/_index.md:92:14": API reference page for 'is_error_code_available<E>' not found, please use an identifier wholly contained in a page title
167 <b>API NOT FOUND IN DOCS <code>is_error_code_available<E></code></b>
168 is true for decayed <code>error_type</code>.</li>
169 <li><code>predicate::enable_compatible_conversion<A, B, C></code> is not true.</li>
170 <li><code>A</code> is <code>void</code> OR <code>value_type</code> is explicitly constructible from <code>A</code>.</li>
171 <li><code>error_type</code> is explicitly constructible from <code>make_error_code(B)</code>.</li>
174 <li><p><code>predicate::enable_make_exception_ptr_compatible_conversion<A, B, C></code> is constexpr boolean true if:</p>
177 <li><code>predicate::constructors_enabled</code> is true.</li>
178 <li><code>basic_result<A, B, C></code> is not this <code>basic_result</code> type.</li>
179 <li>Trait "/home/travis/build/ned14/boost-outcome/doc/src/content/reference/types/basic_result/_index.md:100:14": API reference page for 'is_exception_ptr_available<E>' not found, please use an identifier wholly contained in a page title
180 <b>API NOT FOUND IN DOCS <code>is_exception_ptr_available<E></code></b>
181 is true for decayed <code>error_type</code>.</li>
182 <li><code>predicate::enable_compatible_conversion<A, B, C></code> is not true.</li>
183 <li><code>A</code> is <code>void</code> OR <code>value_type</code> is explicitly constructible from <code>A</code>.</li>
184 <li><code>error_type</code> is explicitly constructible from <code>make_exception_ptr(B)</code>.</li>
187 <li><p><code>predicate::enable_inplace_value_constructor<Args...></code> is constexpr boolean true if:</p>
190 <li><code>predicate::constructors_enabled</code> is true.</li>
191 <li><code>value_type</code> is <code>void</code> OR <code>value_type</code> is explicitly constructible from <code>Args...</code>.</li>
194 <li><p><code>predicate::enable_inplace_error_constructor<Args...></code> is constexpr boolean true if:</p>
197 <li><code>predicate::constructors_enabled</code> is true.</li>
198 <li><code>error_type</code> is <code>void</code> OR <code>error_type</code> is explicitly constructible from <code>Args...</code>.</li>
201 <li><p><code>predicate::enable_inplace_value_error_constructor<Args...></code> is constexpr boolean true if:</p>
204 <li><code>predicate::constructors_enabled</code> is true.</li>
205 <li><code>predicate::implicit_constructors_enabled</code> is true.</li>
206 <li>Either, but not both, of <code>value_type</code> is explicitly constructible from <code>Args...</code> or <code>error_type</code> is explicitly constructible from <code>Args...</code>.</li>
210 <h4 id="summary-of-standard-requirements-provided-https-en-cppreference-com-w-cpp-named-req">Summary of <a href="https://en.cppreference.com/w/cpp/named_req">standard requirements provided</a></h4>
213 <li><del><code>DefaultConstructible</code></del>, always deleted to force user to choose valued or errored for every result instanced.</li>
214 <li><code>MoveConstructible</code>, if both <code>value_type</code> and <code>error_type</code> implement move constructors.</li>
215 <li><code>CopyConstructible</code>, if both <code>value_type</code> and <code>error_type</code> implement copy constructors.</li>
216 <li><code>MoveAssignable</code>, if both <code>value_type</code> and <code>error_type</code> implement move constructors and move assignment.</li>
217 <li><code>CopyAssignable</code>, if both <code>value_type</code> and <code>error_type</code> implement copy constructors and copy assignment.</li>
218 <li><code>Destructible</code>.</li>
219 <li><code>TriviallyCopyable</code>, if both <code>value_type</code> and <code>error_type</code> are trivially copyable.</li>
220 <li><code>TrivialType</code>, if both <code>value_type</code> and <code>error_type</code> are trivial types.</li>
221 <li><code>LiteralType</code>, if both <code>value_type</code> and <code>error_type</code> are literal types.</li>
223 <li><p><code>StandardLayoutType</code>, if both <code>value_type</code> and <code>error_type</code> are standard layout types. If so, layout of <code>basic_result</code> in C is guaranteed to be:</p>
224 <div class="highlight"><pre class="chroma"><code class="language-c++" data-lang="c++"><span class="k">struct</span> <span class="n">result_layout</span> <span class="p">{</span>
225 <span class="n">value_type</span> <span class="n">value</span><span class="p">;</span>
226 <span class="kt">unsigned</span> <span class="kt">int</span> <span class="n">flags</span><span class="p">;</span>
227 <span class="n">error_type</span> <span class="n">error</span><span class="p">;</span>
228 <span class="p">};</span>
229 </code></pre></div></li>
231 <li><p><code>EqualityComparable</code>, if both <code>value_type</code> and <code>error_type</code> implement equality comparisons with one another.</p></li>
233 <li><p><del><code>LessThanComparable</code></del>, not implemented due to availability of implicit conversions from <code>value_type</code> and <code>error_type</code>, this can cause major surprise (i.e. hard to diagnose bugs), so we don’t implement these at all.
234 ~ <code>Swappable</code></p></li>
236 <li><p><del><code>Hash</code></del>, not implemented as a generic implementation of a unique hash for non-valued items which are unequal would require a dependency on RTTI being enabled.</p></li>
239 <p>Thus <code>basic_result</code> meets the <code>Regular</code> concept if both <code>value_type</code> and <code>error_type</code> are <code>Regular</code>, except for the lack of a default constructor. Often where one needs a default constructor, wrapping <code>basic_result</code> into
240 <a href="https://en.cppreference.com/w/cpp/utility/optional" class="api-reference" target="_blank"><i class="fa fa-book" aria-hidden="true"></i> <code>std::optional<T></code></a>
243 <h3 id="public-member-functions">Public member functions</h3>
245 <h4 id="disabling-constructors">Disabling constructors</h4>
247 <ol class="children children-li"><li>
248 <a href="../../reference/types/basic_result/disabling_catchall.html" ><code>basic_result(Args...) = delete</code></a>
249 <p>Disabling catchall constructor used to give useful diagnostic error when trying to use non-inplace constructors when <code>predicate::constructors_enabled</code> is false.</p><li>
250 <a href="../../reference/types/basic_result/disabling_implicit_constructor.html" ><code>basic_result(X &&) = delete</code></a>
251 <p>Disabling implicit constructor used to give useful diagnostic error when trying to use implicit constructors when <code>predicate::implicit_constructors_enabled</code> is false.</p></li></ol>
253 <h4 id="copy-and-move-constructors-and-assignment-and-destructor">Copy and move constructors and assignment, and destructor</h4>
255 <ol class="children children-li"><li>
256 <a href="../../reference/types/basic_result/default.html" ><code>basic_result() = delete</code></a>
257 <p>The default constructor (disabled).</p><li>
258 <a href="../../reference/types/basic_result/move_constructor.html" ><code>basic_result(basic_result &&)</code></a>
259 <p>Move constructor. Constexpr, triviality and noexcept propagating.</p><li>
260 <a href="../../reference/types/basic_result/copy_constructor.html" ><code>basic_result(const basic_result &)</code></a>
261 <p>Copy constructor. Constexpr, triviality and noexcept propagating.</p><li>
262 <a href="../../reference/types/basic_result/move_assignment.html" ><code>basic_result &operator=(basic_result &&)</code></a>
263 <p>Move assignment. Constexpr, triviality and noexcept propagating.</p><li>
264 <a href="../../reference/types/basic_result/copy_assignment.html" ><code>basic_result &operator=(const basic_result &)</code></a>
265 <p>Copy assignment. Constexpr, triviality and noexcept propagating.</p><li>
266 <a href="../../reference/types/basic_result/destructor.html" ><code>~basic_result()</code></a>
267 <p>Destructor. Constexpr, triviality and noexcept propagating.</p></li></ol>
269 <h4 id="converting-constructors">Converting constructors</h4>
271 <ol class="children children-li"><li>
272 <a href="../../reference/types/basic_result/implicit_value_converting_constructor.html" ><code>basic_result(R &&)</code></a>
273 <p>Implicit <code>value_type</code> constructor. Available if <code>predicate::enable_value_converting_constructor<R></code> is true. Constexpr, triviality and noexcept propagating.</p><li>
274 <a href="../../reference/types/basic_result/implicit_error_converting_constructor.html" ><code>basic_result(S &&)</code></a>
275 <p>Implicit <code>error_type</code> constructor. Available if <code>predicate::enable_error_converting_constructor<S></code> is true. Constexpr, triviality and noexcept propagating.</p><li>
276 <a href="../../reference/types/basic_result/implicit_error_condition_converting_constructor.html" ><code>basic_result(ErrorCondEnum &&)</code></a>
277 <p>Implicit <code>error_type</code> from <code>ErrorCondEnum</code> constructor. Available if <code>predicate::enable_error_condition_converting_constructor<ErrorCondEnum></code> is true. Constexpr, triviality and noexcept propagating.</p><li>
278 <a href="../../reference/types/basic_result/explicit_valueorerror_converting_constructor.html" ><code>explicit basic_result(ValueOrError<T, E> &&)</code></a>
279 <p>Explicit converting constructor from <code>ValueOrError<T, E></code> concept matching types. Available if <code>convert::value_or_error<></code> permits it. Constexpr, triviality and noexcept propagating.</p><li>
280 <a href="../../reference/types/basic_result/explicit_copy_converting_constructor.html" ><code>explicit basic_result(const basic_result<R, S, P> &)</code></a>
281 <p>Explicit converting copy constructor from compatible <code>basic_result</code>. Available if <code>predicate::enable_compatible_conversion<R, S, P></code> is true. Constexpr, triviality and noexcept propagating.</p><li>
282 <a href="../../reference/types/basic_result/explicit_move_converting_constructor.html" ><code>explicit basic_result(basic_result<R, S, P> &&)</code></a>
283 <p>Explicit converting move constructor from compatible <code>basic_result</code>. Available if <code>predicate::enable_compatible_conversion<R, S, P></code> is true. Constexpr, triviality and noexcept propagating.</p><li>
284 <a href="../../reference/types/basic_result/explicit_make_error_code_copy_converting_constructor.html" ><code>explicit basic_result(const basic_result<R, S, P> &)</code></a>
285 <p>Explicit converting copy constructor from compatible <code>basic_result</code>. Available if <code>predicate::enable_make_error_code_compatible_conversion<R, S, P></code> is true. Constexpr, triviality and noexcept propagating.</p><li>
286 <a href="../../reference/types/basic_result/explicit_make_error_code_move_converting_constructor.html" ><code>explicit basic_result(basic_result<R, S, P> &&)</code></a>
287 <p>Explicit converting move constructor from compatible <code>basic_result</code>. Available if <code>predicate::enable_make_error_code_compatible_conversion<R, S, P></code> is true. Constexpr, triviality and noexcept propagating.</p><li>
288 <a href="../../reference/types/basic_result/explicit_make_exception_ptr_copy_converting_constructor.html" ><code>explicit basic_result(const basic_result<R, S, P> &)</code></a>
289 <p>Explicit converting copy constructor from compatible <code>basic_result</code>. Available if <code>predicate::enable_make_exception_ptr_compatible_conversion<R, S, P></code> is true. Constexpr, triviality and noexcept propagating.</p><li>
290 <a href="../../reference/types/basic_result/explicit_make_exception_ptr_move_converting_constructor.html" ><code>explicit basic_result(basic_result<R, S, P> &&)</code></a>
291 <p>Explicit converting move constructor from compatible <code>basic_result</code>. Available if <code>predicate::enable_make_exception_ptr_compatible_conversion<R, S, P></code> is true. Constexpr, triviality and noexcept propagating.</p></li></ol>
293 <h4 id="inplace-constructors">Inplace constructors</h4>
295 <ol class="children children-li"><li>
296 <a href="../../reference/types/basic_result/explicit_inplace_value_constructor.html" ><code>explicit basic_result(in_place_type_t<value_type_if_enabled>, Args ...)</code></a>
297 <p>Explicit inplace value constructor. Available if <code>predicate::enable_inplace_value_constructor<Args ...></code> is true. Constexpr, triviality and noexcept propagating.</p><li>
298 <a href="../../reference/types/basic_result/explicit_inplace_value_constructor_il.html" ><code>explicit basic_result(in_place_type_t<value_type_if_enabled>, std::initializer_list<U>, Args ...)</code></a>
299 <p>Explicit inplace value constructor. Available if <code>predicate::enable_inplace_value_constructor<std::initializer_list<U>, Args ...></code> is true. Constexpr, triviality and noexcept propagating.</p><li>
300 <a href="../../reference/types/basic_result/explicit_inplace_error_constructor.html" ><code>explicit basic_result(in_place_type_t<error_type_if_enabled>, Args ...)</code></a>
301 <p>Explicit inplace error constructor. Available if <code>predicate::enable_inplace_error_constructor<Args ...></code> is true. Constexpr, triviality and noexcept propagating.</p><li>
302 <a href="../../reference/types/basic_result/explicit_inplace_error_constructor_il.html" ><code>explicit basic_result(in_place_type_t<error_type_if_enabled>, std::initializer_list<U>, Args ...)</code></a>
303 <p>Explicit inplace error constructor. Available if <code>predicate::enable_inplace_error_constructor<std::initializer_list<U>, Args ...></code> is true. Constexpr, triviality and noexcept propagating.</p><li>
304 <a href="../../reference/types/basic_result/implicit_inplace_value_error_constructor.html" ><code>basic_result(A1 &&, A2 &&, Args ...)</code></a>
305 <p>Implicit inplace value or error constructor. Available if <code>predicate::enable_inplace_value_error_constructor<A1, A2, Args ...></code> is true. Constexpr, triviality and noexcept propagating.</p></li></ol>
307 <h4 id="tagged-constructors">Tagged constructors</h4>
309 <ol class="children children-li"><li>
310 <a href="../../reference/types/basic_result/implicit_success_copy_constructor.html" ><code>basic_result(const success_type<T> &)</code></a>
311 <p>Implicit value-from-success-type-sugar copy constructor. Available if <code>predicate::enable_compatible_conversion<T, void, void></code> is true, or <code>T</code> is <code>void</code>. Constexpr, triviality and noexcept propagating.</p><li>
312 <a href="../../reference/types/basic_result/implicit_success_move_constructor.html" ><code>basic_result(success_type<T> &&)</code></a>
313 <p>Implicit value-from-success-type-sugar move constructor. Available if <code>predicate::enable_compatible_conversion<T, void, void></code> is true, or <code>T</code> is <code>void</code>. Constexpr, triviality and noexcept propagating.</p><li>
314 <a href="../../reference/types/basic_result/implicit_failure_copy_constructor.html" ><code>basic_result(const failure_type<T> &)</code></a>
315 <p>Implicit error-from-failure-type-sugar copy constructor. Available if <code>predicate::enable_compatible_conversion<void, T, void></code> is true, or <code>T</code> is <code>void</code>. Constexpr, triviality and noexcept propagating.</p><li>
316 <a href="../../reference/types/basic_result/implicit_failure_move_constructor.html" ><code>basic_result(failure_type<T> &&)</code></a>
317 <p>Implicit error-from-failure-type-sugar move constructor. Available if <code>predicate::enable_compatible_conversion<void, T, void></code> is true, or <code>T</code> is <code>void</code>. Constexpr, triviality and noexcept propagating.</p><li>
318 <a href="../../reference/types/basic_result/implicit_failure_make_error_code_copy_constructor.html" ><code>basic_result(const failure_type<T> &)</code></a>
319 <p>Implicit error-from-failure-type-sugar copy constructor. Available if <code>predicate::enable_make_error_code_compatible_conversion<void, T, void></code> is true, or <code>T</code> is <code>void</code>. Constexpr, triviality and noexcept propagating.</p><li>
320 <a href="../../reference/types/basic_result/implicit_failure_make_error_code_move_constructor.html" ><code>basic_result(failure_type<T> &&)</code></a>
321 <p>Implicit error-from-failure-type-sugar move constructor. Available if <code>predicate::enable_make_error_code_compatible_conversion<void, T, void></code> is true, or <code>T</code> is <code>void</code>. Constexpr, triviality and noexcept propagating.</p><li>
322 <a href="../../reference/types/basic_result/implicit_failure_make_exception_ptr_copy_constructor.html" ><code>basic_result(const failure_type<T> &)</code></a>
323 <p>Implicit error-from-failure-type-sugar copy constructor. Available if <code>predicate::enable_make_exception_ptr_compatible_conversion<void, T, void></code> is true, or <code>T</code> is <code>void</code>. Constexpr, triviality and noexcept propagating.</p><li>
324 <a href="../../reference/types/basic_result/implicit_failure_make_exception_ptr_move_constructor.html" ><code>basic_result(failure_type<T> &&)</code></a>
325 <p>Implicit error-from-failure-type-sugar move constructor. Available if <code>predicate::enable_make_exception_ptr_compatible_conversion<void, T, void></code> is true, or <code>T</code> is <code>void</code>. Constexpr, triviality and noexcept propagating.</p></li></ol>
327 <h4 id="observers">Observers</h4>
329 <ol class="children children-li"><li>
330 <a href="../../reference/types/basic_result/operator_bool.html" ><code>explicit operator bool() const noexcept</code></a>
331 <p>Returns true if a value is present. Constexpr, never throws.</p><li>
332 <a href="../../reference/types/basic_result/has_value.html" ><code>bool has_value() const noexcept</code></a>
333 <p>Returns true if a value is present. Constexpr, never throws.</p><li>
334 <a href="../../reference/types/basic_result/has_error.html" ><code>bool has_error() const noexcept</code></a>
335 <p>Returns true if an error is present. Constexpr, never throws.</p><li>
336 <a href="../../reference/types/basic_result/has_exception.html" ><code>bool has_exception() const noexcept</code></a>
337 <p>Always returns false for <code>basic_result</code>. Constexpr, never throws.</p><li>
338 <a href="../../reference/types/basic_result/has_failure.html" ><code>bool has_failure() const noexcept</code></a>
339 <p>Returns true if there is either an error or an exception. Constexpr, never throws.</p><li>
340 <a href="../../reference/types/basic_result/has_lost_consistency.html" ><code>bool has_lost_consistency() const noexcept</code></a>
341 <p>Returns true if a preceding swap involving this object failed to preserve the strong guarantee. Constexpr, never throws.</p><li>
342 <a href="../../reference/types/basic_result/assume_value_lvalue.html" ><code>value_type &assume_value() & noexcept</code></a>
343 <p>Narrow contract lvalue reference observer of any value present. Constexpr propagating, never throws.</p><li>
344 <a href="../../reference/types/basic_result/assume_value_lvalue_const.html" ><code>const value_type &assume_value() const & noexcept</code></a>
345 <p>Narrow contract const lvalue reference observer of any value present. Constexpr propagating, never throws.</p><li>
346 <a href="../../reference/types/basic_result/assume_value_rvalue.html" ><code>value_type &&assume_value() && noexcept</code></a>
347 <p>Narrow contract rvalue reference observer of any value present. Constexpr propagating, never throws.</p><li>
348 <a href="../../reference/types/basic_result/assume_value_rvalue_const.html" ><code>const value_type &&assume_value() const && noexcept</code></a>
349 <p>Narrow contract const rvalue reference observer of any value present. Constexpr propagating, never throws.</p><li>
350 <a href="../../reference/types/basic_result/value_lvalue.html" ><code>value_type &value() &</code></a>
351 <p>Wide contract lvalue reference observer of any value present. Constexpr propagating.</p><li>
352 <a href="../../reference/types/basic_result/value_lvalue_const.html" ><code>const value_type &value() const &</code></a>
353 <p>Wide contract const lvalue reference observer of any value present. Constexpr propagating.</p><li>
354 <a href="../../reference/types/basic_result/value_rvalue.html" ><code>value_type &&value() &&</code></a>
355 <p>Wide contract rvalue reference observer of any value present. Constexpr propagating.</p><li>
356 <a href="../../reference/types/basic_result/value_rvalue_const.html" ><code>const value_type &&value() const &&</code></a>
357 <p>Wide contract const rvalue reference observer of any value present. Constexpr propagating.</p><li>
358 <a href="../../reference/types/basic_result/assume_error_lvalue.html" ><code>error_type &assume_error() & noexcept</code></a>
359 <p>Narrow contract lvalue reference observer of the stored error. Constexpr propagating, never throws.</p><li>
360 <a href="../../reference/types/basic_result/assume_error_lvalue_const.html" ><code>const error_type &assume_error() const & noexcept</code></a>
361 <p>Narrow contract const lvalue reference observer of the stored error. Constexpr propagating, never throws.</p><li>
362 <a href="../../reference/types/basic_result/assume_error_rvalue.html" ><code>error_type &&assume_error() && noexcept</code></a>
363 <p>Narrow contract rvalue reference observer of the stored error. Constexpr propagating, never throws.</p><li>
364 <a href="../../reference/types/basic_result/assume_error_rvalue_const.html" ><code>const error_type &&assume_error() const && noexcept</code></a>
365 <p>Narrow contract const rvalue reference observer of the stored error. Constexpr propagating, never throws.</p><li>
366 <a href="../../reference/types/basic_result/error_lvalue.html" ><code>error_type &error() &</code></a>
367 <p>Wide contract lvalue reference observer of the stored error. Constexpr propagating.</p><li>
368 <a href="../../reference/types/basic_result/error_lvalue_const.html" ><code>const error_type &error() const &</code></a>
369 <p>Wide contract const lvalue reference observer of the stored error. Constexpr propagating.</p><li>
370 <a href="../../reference/types/basic_result/error_rvalue.html" ><code>error_type &&error() &&</code></a>
371 <p>Wide contract rvalue reference observer of the stored error. Constexpr propagating.</p><li>
372 <a href="../../reference/types/basic_result/error_rvalue_const.html" ><code>const error_type &&error() const &&</code></a>
373 <p>Wide contract const rvalue reference observer of the stored error. Constexpr propagating.</p><li>
374 <a href="../../reference/types/basic_result/as_failure_lvalue.html" ><code>auto as_failure() const &</code></a>
375 <p>Return the output from free function <code>failure()</code> containing a copy of any errored state.</p></li></ol>
377 <h4 id="modifiers">Modifiers</h4>
379 <ol class="children children-li"><li>
380 <a href="../../reference/types/basic_result/swap.html" ><code>void swap(basic_result &)</code></a>
381 <p>Swap one basic_result with another, with the strong guarantee. Noexcept propagating.</p><li>
382 <a href="../../reference/types/basic_result/as_failure_rvalue.html" ><code>auto as_failure() &&</code></a>
383 <p>Return the output from free function <code>failure()</code> containing a move of any errored state.</p></li></ol>
385 <h4 id="comparisons">Comparisons</h4>
387 <p>See above for why <code>LessThanComparable</code> is not implemented.</p>
389 <ol class="children children-li"><li>
390 <a href="../../reference/types/basic_result/equality_basic_result.html" ><code>bool operator==(const basic_result<A, B, C> &) const</code></a>
391 <p>Returns true if this result compares equal to the other result. Constexpr and noexcept propagating.</p><li>
392 <a href="../../reference/types/basic_result/inequality_success_type.html" ><code>bool operator==(const success_type<A> &) const</code></a>
393 <p>Returns true if this result compares equal to the success type sugar. Constexpr and noexcept propagating.</p><li>
394 <a href="../../reference/types/basic_result/equality_failure_type.html" ><code>bool operator==(const failure_type<A, void> &) const</code></a>
395 <p>Returns true if this result compares equal to the failure type sugar. Constexpr and noexcept propagating.</p><li>
396 <a href="../../reference/types/basic_result/inequality_basic_result.html" ><code>bool operator!=(const basic_result<A, B, C> &) const</code></a>
397 <p>Returns true if this result does not compare equal to the other result. Constexpr and noexcept propagating.</p><li>
398 <a href="../../reference/types/basic_result/equality_success_type.html" ><code>bool operator!=(const success_type<A> &) const</code></a>
399 <p>Returns true if this result does not compare equal to the success type sugar. Constexpr and noexcept propagating.</p><li>
400 <a href="../../reference/types/basic_result/inequality_failure_type.html" ><code>bool operator!=(const failure_type<A, void> &) const</code></a>
401 <p>Returns true if this result does not compare equal to the failure type sugar. Constexpr and noexcept propagating.</p></li></ol>
409 </div><p><small>Last revised: October 11, 2019 at 17:03:05 +0100</small></p>
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