title: Do we have C++20 ranges library in GCC 9?
body: <p>Do we have support for C++20 ranges library in the newly released GCC 9?</p>
  
  <p>I copied the example code below for ranges library from: 
  <a href="https://en.cppreference.com/w/cpp/ranges" rel="noreferrer">https://en.cppreference.com/w/cpp/ranges</a></p>
  
  <pre><code>#include &lt;vector&gt;
  #include &lt;ranges&gt;
  #include &lt;iostream&gt;
  
  int main()
  {
    std::vector&lt;int&gt; ints{0,1,2,3,4,5};
    auto even = [](int i){ return 0 == i % 2; };
    auto square = [](int i) { return i * i; };
  
    for (int i : ints | std::view::filter(even) | std::view::transform(square)) {
      std::cout &lt;&lt; i &lt;&lt; ' ';
    }
  }
  </code></pre>
  
  <p>But when compiled with g++ 9.1 (Ubuntu 18.04 LTS  (Bionic Beaver)), it complains that <code>&lt;ranges&gt;</code> cannot be found:</p>
  
  <pre><code>$ g++ -std=c++2a cpp2a.cpp 
  cpp2a.cpp:2:10: fatal error: ranges: No such file or directory
      2 | #include &lt;ranges&gt;
        |          ^~~~~~~~
  compilation terminated.
  </code></pre>
  
  <p>Am I missing something?</p>
  
  <p>And will the ranges library arrive at some point of time with the GCC 9 series?</p>