<p><a href="https://github.com/rcurtin" class="user-mention">@rcurtin</a>: Thanks for the suggestion. I've been thinking about how to most cleanly implement this feature.</p>

<p>The approach via variadic templates is interesting, but making that work would probably require some <a href="http://stackoverflow.com/questions/27941661">template black magic</a>. Now appetites for these things vary, but that's a bit much for me. Or maybe you had something else in mind?</p>

<p>What do you think about using either a traditional inheritence-based approach or <code>std::function</code>? There is some additional runtime overhead compared to templates, but it should be negligible compared to the linear algebra.</p>

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