<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div>First, I’d like to thank <a href="https://github.com/oisdk" class="">Oisin</a> for his proposal. It’s great to see people filling in gaps.</div><div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><div class=""><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>* What is your evaluation of the proposal?<br class=""></div></div></div></div></div></blockquote><div><br class=""></div>The basic idea is solid and obviously appropriate. I have some quibbles with the proposed solution.</div><div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><div class=""><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>* Is the problem being addressed significant enough to warrant a change to Swift?<br class=""></div></div></div></div></div></blockquote><div><br class=""></div>Yes; it’s a non-uniformity, nonuniformities create complexity for users.</div><div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><div class=""><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>* Does this proposal fit well with the feel and direction of Swift?<br class=""></div></div></div></div></div></blockquote><div><br class=""></div>Yes.</div><div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><div class=""><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>* How much effort did you put into your review? A glance, a quick reading, or an in-depth study?</div></div></div></div></div></blockquote><div><br class=""></div>A quick reading, but I’m deeply familiar with the domain, having written the lazy facilities we have in the stdlib.</div><div><br class=""></div><div>I don’t see why the proposal states, “<code style="color: rgb(51, 51, 51); box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Optional</code><span style="color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);" class=""> </span><em style="color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255); box-sizing: border-box;" class="">probably</em><span style="color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);" class=""> wouldn't have a </span><code style="color: rgb(51, 51, 51); box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">BidirectionalIndexType</code>“. It seems to me that as a collection, an optional’s index should be random access, just like CollectionOfOne’s.</div><div><br class=""></div><div>I’d like to suggest a different implementation approach that not only handles the bidirectional issue but also probably reduces the amount of code involved: create a generic <font face="Menlo" class="">CollectionOfZeroOrOne<T></font> that wraps a <font face="Menlo" class="">T?</font>, and implement the <font face="Menlo" class="">x.flatmap(f)</font> where <font face="Menlo" class="">f</font> returns an optional as <font face="Menlo" class="">x.flatmap { CollectionOfZeroOrOne(f($0)) }</font></div><div><br class=""></div><div>What do you think?</div><div><br class=""></div><div class="">
-Dave<div class=""><br class=""></div><br class="Apple-interchange-newline">
</div>
<br class=""></body></html>