I am wondering what the best pattern/approach for a data structure that may contain either a reference or a copy of some data used in a constructor. &nbsp;I would love the opportunity to have the data structure capable of conditionally storing the data for the data copy on the stack. &nbsp;Are there any fancy generic tricks/patterns to do this using boost::mpl, etc.?<div>

<div><br></div><div>So to put in some pseudocode notes for discussion to get the point across of what I think I want:<br></div><div><br></div><div>boost::array&lt; boost::array&lt;double, M&gt;, N&gt; myaxis; //creates axis in a stack allocated data structure.</div>
<div>regular_grid&lt;M, N, COPYDATA&gt; my_grid(axis_values);<br>
</div><div>regular_grid&lt;M, N, REFDATA&gt; my_grid(axis_values);<br></div><div><br></div><div>template&lt;int M, int N, int ConstructionPolicy&gt;</div><div>class regular_grid</div><div>{</div><div>&nbsp;&nbsp; &nbsp; boost::array&lt; boost::array&lt;double, M&gt;, N&gt;&amp; axis_ref_; //Reference to the axis, either static or actual reference. &nbsp;All code in the class would use this, not axis_<br>
</div><div><div></div></div><div><br></div><div>&nbsp;&nbsp; &nbsp;STATIC_IF(ConstructionPolicy ==&nbsp;COPYDATA)</div><div>&nbsp;&nbsp; &nbsp; {</div><div>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;&nbsp;boost::array&lt; boost::array&lt;double, M&gt;, N&gt; axis_;</div><div><div>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;regular_grid(const&nbsp;boost::array&lt; boost::array&lt;double, M&gt;, N&gt;&amp; axis) : axis_(axis), axis_ref_(axis_) //constructor makes copy, sets ref to copy.</div>
<div>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; {</div><div>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }</div><div><br></div></div><div>&nbsp;&nbsp; &nbsp; }</div><div>&nbsp;&nbsp; &nbsp;STATIC_ELSE(ConstructionPolicy == REFDATA)<br></div><div><div>&nbsp;&nbsp; &nbsp;{</div><div>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;regular_grid(const&nbsp;boost::array&lt; boost::array&lt;double, M&gt;, N&gt;&amp; axis) : axis_ref_(axis) {} //constructor just uses the ref.<br>
</div><div>&nbsp;&nbsp; &nbsp;}</div></div><div>};</div><div>
<br></div><div>Is this possible? &nbsp;any ideas on code to look at to see how to do it?</div>
<div><br></div>
</div>