<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">I noticed that the new Collection<a class="toggle-link" data-toggle="collapse" href="http://swiftdoc.org/v3.0/protocol/Collection/#comment-func-index_offsetby_" style="box-sizing: border-box; color: rgb(153, 153, 153); text-decoration: none; line-height: 18px; font-family: Menlo, Consolas, monospace; display: inline-block; margin-left: 25px; text-indent: -25px; background-position: 0px 0px;"> <span class="identifier" style="box-sizing: border-box; color: rgb(111, 65, 167);">index</span>(<wbr style="box-sizing: border-box;" class="">_:<wbr style="box-sizing: border-box;" class="">offsetBy:)</a><span style="font-size: 10px;" class=""> </span>does not define that negative offsets require a BidirectionalCollection. It also declares that negative offsets must complete in O( | offset | ) time. This differs from other methods such as<a class="toggle-link" data-toggle="collapse" href="http://swiftdoc.org/v3.0/protocol/Collection/#comment-func-distance-from_to_" style="box-sizing: border-box; color: rgb(153, 153, 153); text-decoration: none; line-height: 18px; font-family: Menlo, Consolas, monospace; display: inline-block; margin-left: 25px; text-indent: -25px; background-position: 0px 0px;"> <span class="identifier" style="box-sizing: border-box; color: rgb(111, 65, 167);">distance</span>(<wbr style="box-sizing: border-box;" class="">from:<wbr style="box-sizing: border-box;" class="">to:)</a>which indicates start <= end if not a BidirectionalCollection<div class=""><br class=""></div><div class="">This would preclude some data structures from strictly implementing the Collection protocol, such as singly-linked lists.</div><div class=""><br class=""></div><div class="">Would it be appropriate to indicate instead that BidirectionalCollection defines the negative offset behavior and negative offset performance constraint?<br class=""><div class=""><br class=""></div><div class="">-DW</div></div></body></html>