On Monday, 24 October 2016, monty &lt;<a href="mailto:monty2@programmer.net">monty2@programmer.net</a>&gt; wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Why not just make #size a subclassResponsibility or add abstract superclasses for lazy or infinite collections that implement #isEmpty using #do: and change #size to shouldNotImplement?<br>
</blockquote><div><br></div><div>Because #do: is the only method required to be overridden by Collection subclasses. All other methods are implemented in terms of #do:.</div><div><br></div><div>So yes, if your Collection subclass has an optimized implementation for #isEmpty, then provide it. That is a small price to pay for making a class work optimally across different code bases.</div><div><br></div><div>- Bert - </div>