lass="identifier">type_name</span></code>. <code class="literal">attribute_type<span class="emphasis"><em>N</em></span></code>
        and <code class="literal">attribute_const_type<span class="emphasis"><em>N</em></span></code> may specify
        the types that <code class="literal">get_expr<span class="emphasis"><em>N</em></span></code> denotes
        to, when omitted the type is deduced from [get_expr<span class="emphasis"><em>N</em></span>]
        return type via BOOST_TYPEOF. On compiler missing sup