gs together.
That function will only be invoked if no <tt class="docutils literal">s3</tt> argument is supplied by
the caller.</p>
<!-- The expression ``lambda::var(s1)+lambda::var(s2)`` yields a -->
<!-- *function object* that, when invoked, adds the two strings -->
<!-- together.  That function will only be invoked if no ``s3`` argument -->
<!-- is supplied by the caller. -->
</div>
</div>
</div>
<div class="section" id="best-practices">
<h1><a class="toc-backref" href="#id34">4&nbsp;&nbsp;&nbsp;Best Prac