Composition of classes
<p>How come, when setting up class composition, contained classes can be called with a default constructor but not with one that takes parameters?</p>

<p>That's kind of confusing; let me offer an example.</p>

<pre><code>#include "A.h"
class B
{
private:
    A legal; // this kind of composition is allowed
    A illegal(2,2); // this kind is not.
};
</code></pre>

<p>Assuming both the default constructor and one that takes 2 integers exists, only one of these is allowed.  Why is this?</p>
