Are C++17 Parallel Algorithms implemented already? : <p>I was trying to play around with the new parallel library features proposed in the C++17 standard, but I couldn't get it to work. I tried compiling with the up-to-date versions of <code>g++ 8.1.1</code> and <code>clang++-6.0</code> and <code>-std=c++17</code>, but neither seemed to support <code>#include &lt;execution&gt;</code>, <code>std::execution::par</code> or anything similar. </p>

<p>When looking at the <a href="https://en.cppreference.com/w/cpp/experimental/parallelism" rel="noreferrer">cppreference</a> for parallel algorithms there is a long list of algorithms, claiming </p>

<blockquote>
  <p>Technical specification provides parallelized versions of the following 69 algorithms from <code>algorithm</code>, <code>numeric</code> and <code>memory</code>: <em>( ... long list ...)</em></p>
</blockquote>

<p>which sounds like the algorithms are ready <em>'on paper'</em>, but not ready to use yet?</p>

<p>In <a href="https://stackoverflow.com/questions/42567998/how-do-i-use-the-new-c17-execution-policies">this SO question</a> from over a year ago the answers claim these features hadn't been implemented yet. But by now I would have expected to see some kind of implementation. Is there anything we can use already?</p>
