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- <div class="titlepage"><div><div><h1 style="clear: both">Built-in policies</h1></div></div></div>
- <p>These are the predefined policies built into Outcome:</p>
- <hr style="border-color: black;">
- <p> </p>
- <a href="../../../reference/policies/all_narrow.html" class="api-reference"><code>all_narrow</code></a>
- <p>If there is an observation of a value/error/exception which is not present,
- the program is put into a <strong>hard undefined behaviour</strong> situation. The
- compiler <em>literally</em> compiles no code for an invalid observation – the
- CPU “runs off” into the unknown.</p>
- <p>As bad as this may sound, it generates the most optimal code, and such
- hard UB is very tool-friendly for detection e.g. undefined behaviour
- sanitiser, valgrind memcheck, etc.</p>
- <p>If you are considering choosing this policy, definitely read
- <a href="../../../reference/policies/base/ub.html" class="api-reference"><code>static void _ub(Impl &&)</code></a>
- first.</p>
- <p>Note that <a href="../../../reference/aliases/unchecked.html" class="api-reference"><code>unchecked<T, E = varies></code></a>
- aliases a <code>basic_result</code>
- with the <code>all_narrow</code> no-value policy.</p>
- <hr style="border-color: black;">
- <p> </p>
- <a href="../../../reference/policies/terminate.html" class="api-reference"><code>terminate</code></a>
- <p>Observation of a missing value/error/exception causes a call to
- <code>std::terminate()</code>.</p>
- <p>Note that configuring <code>EC = void</code> or <code>EP = void</code> causes
- <a href="../../../reference/aliases/default_policy.html" class="api-reference"><code>default_policy</code></a>
- to choose <code>terminate</code> as the no-value policy.</p>
- <hr style="border-color: black;">
- <p> </p>
- <a href="../../../reference/policies/error_code_throw_as_system_error_outcome.html" class="api-reference"><code>error_code_throw_as_system_error<T, EC, EP></code></a>
- <p>This policy assumes that <code>EC</code> has the interface of <code>std::error_code</code>,
- and <code>EP</code> has the interface of <code>std::exception_ptr</code>. Upon missing value
- observation:</p>
- <ul>
- <li>if an exception is stored through pointer of type <code>EP</code> it is rethrown;</li>
- <li>otherwise, if an error of type <code>EC</code> is stored, it is converted to <code>error_code</code>
- and then thrown as <code>system_error</code>.</li>
- </ul>
- <p>Upon missing error observation throws:</p>
- <ul>
- <li><code>bad_result_access("no error")</code> from instances of <code>basic_result<></code>.</li>
- <li><code>bad_outcome_access("no error")</code> from instances of <code>basic_outcome<></code>.</li>
- </ul>
- <p>Upon missing exception observation throws <code>bad_outcome_access("no exception")</code>.</p>
- <p>Overloads are provided for <code>boost::system::error_code</code> and <code>boost::exception_ptr</code>.</p>
- <p>Note that if <a href="../../../reference/traits/is_error_code_available.html" class="api-reference"><code>is_error_code_available<T></code></a>
- is true for <code>EC</code>,
- and (if <code>basic_outcome</code>) <a href="../../../reference/traits/is_exception_ptr_available.html" class="api-reference"><code>is_exception_ptr_available<T></code></a>
- is true for <code>EP</code>, <a href="../../../reference/aliases/default_policy.html" class="api-reference"><code>default_policy</code></a>
- chooses
- <code>error_code_throw_as_system_error<T, EC, EP></code> as the no-value policy.</p>
- <hr style="border-color: black;">
- <p> </p>
- <a href="../../../reference/policies/exception_ptr_rethrow_outcome.html" class="api-reference"><code>exception_ptr_rethrow<T, EC, EP></code></a>
- <p>This policy assumes that either <code>EC</code> or <code>EP</code> (unless <code>void</code>) has the interface of <code>std::exception_ptr</code>. Upon missing value observation:</p>
- <ul>
- <li>in instances of <code>basic_result<></code>, rethrows exception pointed to by <code>EC</code>;</li>
- <li>in instances of <code>basic_outcome<></code>, if exception <code>EP</code> is present rethrows it,
- otherwise rethrows <code>EC</code>.</li>
- </ul>
- <p>Upon missing error observation:</p>
- <ul>
- <li>in instances of <code>basic_result<></code>, throws <code>bad_result_access("no error")</code> ;</li>
- <li>in instances of <code>basic_outcome<></code>, throws <code>bad_outcome_access("no error")</code>.</li>
- </ul>
- <p>Upon missing exception observation throws <code>bad_outcome_access("no exception")</code>.</p>
- <p>Overloads are provided for <code>boost::exception_ptr</code>.</p>
- <p>Note that if <a href="../../../reference/traits/is_exception_ptr_available.html" class="api-reference"><code>is_exception_ptr_available<T></code></a>
- is true for <code>EC</code>,
- or (if <code>basic_outcome</code>) <a href="../../../reference/traits/is_exception_ptr_available.html" class="api-reference"><code>is_exception_ptr_available<T></code></a>
- is true for <code>EP</code>, <a href="../../../reference/aliases/default_policy.html" class="api-reference"><code>default_policy</code></a>
- chooses
- <code>exception_ptr_rethrow<T, EC, EP></code> as the no-value policy.</p>
- <hr style="border-color: black;">
- <p> </p>
- <a href="../../../reference/policies/throw_bad_result_access.html" class="api-reference"><code>throw_bad_result_access<EC></code></a>
- <p>Upon missing value observation throws <code>bad_result_access_with<EC>(ec)</code>,
- where <code>ec</code> is the value of the stored error. If error is not stored,
- the behaviour is undefined.</p>
- <p>Upon missing error observation throws <code>bad_result_access("no error")</code>.</p>
- <p>This policy can be used with <code>basic_outcome<></code> instances, where it always
- throws <code>bad_outcome_access</code> for all no-value/error/exception observations.</p>
- <p>Note that <a href="../../../reference/aliases/checked.html" class="api-reference"><code>checked<T, E = varies></code></a>
- aliases a <code>basic_result</code>
- with the <code>throw_bad_result_access<EC></code> no-value policy.</p>
- </div><p><small>Last revised: February 09, 2019 at 15:18:26 UTC</small></p>
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