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- <div class="titlepage"><div><div><h1 style="clear: both">Worked example: Custom domain</h1></div></div></div>
- <p>Here follows a worked example of use of Experimental Outcome. It presents
- the same sample program I sent to the San Diego 2018 WG21 standards meeting
- after I was asked by the committee to demonstrate how P1095 implements P0709
- in a working code example they could study and discuss.</p>
- <p>We will walk through this worked example, step by step, explaining how each
- part works in detail. This will help you implement your own code based on
- Experimental Outcome.</p>
- <p>You may find it useful to open now in a separate browser tab the reference API
- documentation for proposed <code><system_error2></code> at <a href="https://ned14.github.io/status-code/">https://ned14.github.io/status-code/</a>
- (scroll half way down). The references in the comments to P1028 are to
- <a href="http://wg21.link/P1028">P1028 <em>SG14 status_code and standard error object for P0709 Zero-overhead
- deterministic exceptions</em></a>, which is the WG21 proposal
- paper for potential <code><system_error2></code>.</p>
- <h3 id="goal-of-this-section">Goal of this section</h3>
- <p>We are going to define a simple custom code domain which defines that
- the status code’s payload will consist of a POSIX error code, and the
- <code>__FILE__</code> and <code>__LINE__</code> where the failure occurred. This custom status
- code will have an implicit conversion to type erased <code>error</code> defined, which dynamically
- allocates memory for the original status code, and outputs an <code>error</code>
- which manages that dynamic allocation, indirecting all queries etc
- to the erased custom status code type such that the <code>error</code> instance
- quacks as if just like the original. This demonstrates that <code>error</code> could
- just as equally convey a <code>std::exception_ptr</code>, for example, or indeed
- manage the lifetime of any pointer.</p>
- </div><p><small>Last revised: January 26, 2019 at 23:38:56 UTC</small></p>
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