title: mpl style copy_if meta-function for variadic template vector
body: <p>I've a meta-program that works fine with the regular boost mpl. It looks more like the following.</p>
  
  <pre><code>template &lt;class Vector, class ResultKind, class Custom&gt;
  struct FilterChildrenIfNotOk
  {
    typedef typename 
      copy_if&lt;Vector, 
              or_&lt;is_same&lt;boost::mpl::placeholders::_1, ResultKind&gt;,
                  IsOk&lt;boost::mpl::placeholders::_1, 
                       ResultKind, 
                       Custom&gt; &gt; &gt;::type type;
  };
  </code></pre>
  
  <p>I'm trying to compile it using variadic templates vector (mpl::vector). For that, I'm using the implementation of variadic templates vector found here: <a href="https://svn.boost.org/svn/boost/sandbox/variadic_templates" rel="nofollow">https://svn.boost.org/svn/boost/sandbox/variadic_templates</a></p>
  
  <p>I could not find usable implementations of copy_if, remove_if, and count_if in the repo, although there are some tests. Are those meta-programs there and I'm just not able to find them? Alternately, can you please help me implement one of them such that it also supports mpl placeholders. Thanks for your help in advance.</p>