How to forward declare the following template class
<p>I try to forward declare concurrent_bounded_queue ;</p>

<pre><code>class MyClass {
    namespace tbb {
        template&lt;typename T&gt; class cache_aligned_allocator;
        template&lt;class T, class A = cache_aligned_allocator&gt; class concurrent_bounded_queue;
    };

    // I wish to maintain this syntax.
    tbb::concurrent_bounded_queue&lt;std::string&gt;&amp; concurrentBoundedQueue;
}
</code></pre>

<hr>

<p>I get the following error :</p>

<pre><code>error C3203: 'cache_aligned_allocator' : unspecialized class template can't be used as a template argument for template parameter 'A', expected a real type
error C2955: 'tbb::cache_aligned_allocator' : use of class template requires template argument list c:\projects\vitroxreport\src\Executor.h(21) : see declaration of 'tbb::cache_aligned_allocator'
</code></pre>

<p>May I know how I can avoid?</p>

<p>Thanks.</p>
