title: C++20 in g++10: generator not defined
body: <p>This MCVE works fine in Visual Studio.</p>
  <pre><code>#include &lt;experimental/generator&gt;
  #include &lt;iostream&gt;
  
  std::experimental::generator&lt;int&gt; f() { for (int i = 0; i &lt; 10; ++i) co_yield i; }
  
  int main ()
  {
      for (int i : f())
          std::cout &lt;&lt; i &lt;&lt; ' ';
  
      return 0;
  }
  </code></pre>
  <p>but in g++10, which is listed as having full support or C++20's coroutines, it does not.</p>
  <p>(Taking out <code>experimental</code> doesn't help.)</p>
  <p>I am compiling thus: <code>g++ -g -std=c++2a -fcoroutines -c main.cpp</code>.</p>
  <p>It complains that there is no include file generator, and if I take out the <code>#include</code>, that generator is not a part of std:: or is not defined. I suppose there's another name for it in the new standard? Or if not, what do I do instead to get a coroutine that uses <code>co_yield</code>?</p>