<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 style="margin: 0px; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 132, 0);" class="">Hi Nevin,</div><div style="margin: 0px; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 132, 0);" class=""><br class=""></div><div style="margin: 0px; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 132, 0);" class=""><div style="margin: 0px; line-height: normal; color: rgb(187, 44, 162);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">extension</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">String</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">{</span></div><p style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);" class="">var</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> count: </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);" class="">Int</span></p><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">get</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">characters</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">count</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">// Sigh... String subscriptors should be already builtin in the String</span></div><p style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">subscript</span><span style="font-variant-ligatures: no-common-ligatures" class=""> (idx: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Int</span><span style="font-variant-ligatures: no-common-ligatures" class="">) -> </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">String</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">get</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; line-height: normal; color: rgb(61, 29, 129);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">.</span><span style="font-variant-ligatures: no-common-ligatures" class="">substringWithRange</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">(</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">startIndex</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3d1d81" class="">advancedBy</span><span style="font-variant-ligatures: no-common-ligatures" class="">(idx)..<</span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">startIndex</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3d1d81" class="">advancedBy</span><span style="font-variant-ligatures: no-common-ligatures" class="">(idx + </span><span style="font-variant-ligatures: no-common-ligatures; color: #272ad8" class="">1</span><span style="font-variant-ligatures: no-common-ligatures" class="">)</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> )</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">// range subscript [n1..n2] or [n1...n2]</span></div><p style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><p style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">subscript</span><span style="font-variant-ligatures: no-common-ligatures" class=""> (r: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Range</span><span style="font-variant-ligatures: no-common-ligatures" class=""><</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Int</span><span style="font-variant-ligatures: no-common-ligatures" class="">>) -> </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">String</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">get</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; line-height: normal; color: rgb(61, 29, 129);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">.</span><span style="font-variant-ligatures: no-common-ligatures" class="">substringWithRange</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">(</span></div><div style="margin: 0px; line-height: normal; color: rgb(112, 61, 170);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">.</span><span style="font-variant-ligatures: no-common-ligatures" class="">startIndex</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3d1d81" class="">advancedBy</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">(r.</span><span style="font-variant-ligatures: no-common-ligatures" class="">startIndex</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">)..<</span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">.</span><span style="font-variant-ligatures: no-common-ligatures" class="">startIndex</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3d1d81" class="">advancedBy</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">(r.</span><span style="font-variant-ligatures: no-common-ligatures" class="">endIndex</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">) )</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">//////////////////////////////////////////////</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">func</span><span style="font-variant-ligatures: no-common-ligatures" class=""> hazPrefix(s: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">String</span><span style="font-variant-ligatures: no-common-ligatures" class="">) -> </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Bool</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">if</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">isEmpty</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> && s.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">isEmpty</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">// both are empty: match</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">true</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">if</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">isEmpty</span><span style="font-variant-ligatures: no-common-ligatures" class=""> || s.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">isEmpty</span><span style="font-variant-ligatures: no-common-ligatures" class=""> ||</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> (s.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">count</span><span style="font-variant-ligatures: no-common-ligatures" class=""> > </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">count</span><span style="font-variant-ligatures: no-common-ligatures" class="">)</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">false</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">var</span><span style="font-variant-ligatures: no-common-ligatures" class=""> match = </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">true</span></div><p style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">for</span><span style="font-variant-ligatures: no-common-ligatures" class=""> i </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">in</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #272ad8" class="">0</span><span style="font-variant-ligatures: no-common-ligatures" class="">..<s.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">count</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">if</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">[</span><span style="font-variant-ligatures: no-common-ligatures" class="">i</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">]</span><span style="font-variant-ligatures: no-common-ligatures" class=""> != s</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">[</span><span style="font-variant-ligatures: no-common-ligatures" class="">i</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">]</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> match = </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">false</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">break</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> match</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">///////////////////////////////////////////</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">} </span><span style="font-variant-ligatures: no-common-ligatures" class="">// end String extensions.</span></div><div style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; color: rgb(209, 47, 27);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> s = </span><span style="font-variant-ligatures: no-common-ligatures" class="">"abcdefghijklmnopqrstuvwxyz"</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> emptystr = </span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">""</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> emptystr2 = </span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">""</span></div><div style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #3d1d81" class="">print</span><span style="font-variant-ligatures: no-common-ligatures" class="">( </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">s</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">hazPrefix</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">"abc"</span><span style="font-variant-ligatures: no-common-ligatures" class="">) ) </span><span style="font-variant-ligatures: no-common-ligatures;" class="">// true</span></div><div style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #3d1d81" class="">print</span><span style="font-variant-ligatures: no-common-ligatures" class="">( </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">s</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">hazPrefix</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">""</span><span style="font-variant-ligatures: no-common-ligatures" class="">) ) </span><span style="font-variant-ligatures: no-common-ligatures;" class="">// false</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #3d1d81" class="">print</span><span style="font-variant-ligatures: no-common-ligatures" class="">( </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">s</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">hazPrefix</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">"Led Zeppelin."</span><span style="font-variant-ligatures: no-common-ligatures" class="">) ) </span><span style="font-variant-ligatures: no-common-ligatures;" class="">// false</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #3d1d81" class="">print</span><span style="font-variant-ligatures: no-common-ligatures" class="">( </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">emptystr</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">hazPrefix</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">"Swift"</span><span style="font-variant-ligatures: no-common-ligatures" class="">) ) </span><span style="font-variant-ligatures: no-common-ligatures;" class="">// false</span></div><div style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; color: rgb(79, 129, 135);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #3d1d81" class="">print</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">(</span><span style="font-variant-ligatures: no-common-ligatures" class="">emptystr</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">hazPrefix</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">(</span><span style="font-variant-ligatures: no-common-ligatures" class="">emptystr</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">) ) </span><span style="font-variant-ligatures: no-common-ligatures; color: #008400" class="">// true</span></div><div style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; min-height: 19px;" class="">Please see further in-line comments below: </div><div style="margin: 0px; line-height: normal; min-height: 19px;" class=""><br class=""></div><div style="margin: 0px; line-height: normal; min-height: 19px;" class="">Kind Regards,</div><div style="margin: 0px; line-height: normal; min-height: 19px;" class="">Ted</div></div><div style="margin: 0px; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 132, 0);" class=""> </div><div style="margin: 0px; font-size: 16px; line-height: normal; font-family: Menlo; min-height: 19px;" class=""><br class=""></div><div><blockquote type="cite" class=""><div class="">On 21.07.2016, at 00:57, Nevin Brackett-Rozinsky <<a href="mailto:nevin.brackettrozinsky@gmail.com" class="">nevin.brackettrozinsky@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" style="font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div class="gmail_extra"><div class="gmail_quote">On Wed, Jul 20, 2016 at 6:32 PM, Ted F.A. van Gaalen via swift-evolution<span class="Apple-converted-space"> </span><span dir="ltr" class=""><<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>></span><span class="Apple-converted-space"> </span>wrote:<br class=""><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex;"><div style="word-wrap: break-word;" class="">Hi,<div class=""><br class=""></div><div class="">Mathematical correct or not: </div><div class=""><br class=""></div><div class="">in case of </div><div class=""> s1.hasPrefix(s2)</div><div class=""> (or any other containment test method) </div><div class=""><br class=""></div><div class="">s1 and s2 are just plain simple instances of String,</div><div class="">nothing more nothing less. </div><div class=""><br class=""></div><div class="">Which is interpreted by me as: </div><div class="">“test if String s1 starts with String s2”</div><div class=""><br class=""></div></div></blockquote><div class=""><br class=""></div><div class="">…which means, “Do the first n characters of s1 match s2, where n is the length of s2?”</div></div></div></div></div></blockquote>Yes,. and of course s1.count <= s2.count. <br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" style="font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div class="gmail_extra"><div class="gmail_quote"><div class=""><br class=""></div><div class="">When s2 is the empty string, n is 0.</div></div></div></div></div></blockquote><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" style="font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div class="gmail_extra"><div class="gmail_quote"><div class=""><br class=""></div><div class="">What are the first 0 characters of s1? Clearly the empty string, since that is the only string with 0 characters.</div><div class=""><br class=""></div><div class="">Do the first 0 characters of s1 match s2? Well they are both the empty string, and ""=="" is true, so…</div><div class=""><br class=""></div><div class="">That would be a resounding “Yes!”</div></div></div></div></div></blockquote>how dumb (for “”.hasPrefix(“”) ), my mistake. (handled correctly imho in code example above)</div><div>however, that is a matter of definition:</div><div>should “search for nothing in nothing” return “true” ??</div><div><br class=""></div><div>Again, Strings to me are just character arrays...</div><div> <br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" style="font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div class="gmail_extra"><div class="gmail_quote"><div class=""><br class=""></div><div class="">Nevin</div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""> </div><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex;"><div style="word-wrap: break-word;" class=""><div class=""></div><div class="">which, to me, implies that one will never find an occurrence</div><div class="">of an empty string within another string,</div><div class="">for the very simple reason that an empty string</div><div class="">does not exist within another string. **</div><div class="">Ergo: “false” is the right evaluation when s2.isEmpty.</div><div class=""><br class=""></div><div class="">** In my mental model, a String is just an array of 0...n characters,</div><div class=""> <span class="Apple-converted-space"> </span>like it is in most languages, very straightforward.</div><div class=""><br class=""></div><div class=""> (returning false) This is exactly the reason why NSString does that, </div><span class=""><div class="">for more than 20 years, why change it?</div><div class=""><br class=""></div></span><div class="">AFAIK no one has complained about this for years, </div><div class="">because imho it is logically sound. </div><div class=""><br class=""></div><div class="">for a compiler this is very easy</div><div class="">all it has to do is to return False</div><div class="">when either s1 or s2 is empty.</div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">Ted</div><div class=""><div class="h5"><div class=""><br class=""></div><div class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On 19.07.2016, at 23:11, Jacob Bandes-Storch <<a href="mailto:jtbandes@gmail.com" target="_blank" class="">jtbandes@gmail.com</a>> wrote:</div><br class=""><div class=""><div dir="ltr" class="">Not that it's needed, but another +1 from me.<div class=""><br class=""></div><div class="">a.hasPrefix(p) should be true iff there exists some string x for which p+x == a. If p == "", then x := a satisfies this, so hasPrefix should return true.</div><div class="gmail_extra"><br clear="all" class=""><div class=""><div data-smartmail="gmail_signature" class=""><div dir="ltr" class=""><div class="">Jacob<br class=""></div></div></div></div><br class=""><div class="gmail_quote">On Tue, Jul 19, 2016 at 1:29 PM, Jaden Geller via swift-evolution<span class="Apple-converted-space"> </span><span dir="ltr" class=""><<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>></span><span class="Apple-converted-space"> </span>wrote:<br class=""><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex;"><div style="word-wrap: break-word;" class="">Both `hasPrefix` and `hasSuffix` are analogous to the more general `hasSubset` function, which would return `true` for the empty set.<div class=""><div class=""><div class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Jul 19, 2016, at 12:32 PM, Bianca via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>> wrote:</div><br class=""><div class=""><div dir="ltr" class=""><span style="color: rgb(33, 33, 33); font-family: 'helvetica neue', helvetica, arial, sans-serif;" class="">> Empty set is a subset of all sets.</span><br style="color: rgb(33, 33, 33); font-family: 'helvetica neue', helvetica, arial, sans-serif;" class=""><br style="color: rgb(33, 33, 33); font-family: 'helvetica neue', helvetica, arial, sans-serif;" class=""><font color="#212121" face="helvetica neue, helvetica, arial, sans-serif" class="">True but all sets certainly do not _contain_ the empty set, which is what might be confusing, as the word "contains" in the context of sets implies that it's a member of the set of characters that make up a String. </font><div class=""><font color="#212121" face="helvetica neue, helvetica, arial, sans-serif" class=""><br class=""></font><div class="gmail_quote"><div dir="ltr" class="">On Tue, Jul 19, 2016 at 12:23 PM Charlie Monroe via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>> wrote:<br class=""></div><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex;"><br class="">> On Jul 19, 2016, at 6:17 PM, Ted F.A. van Gaalen via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>> wrote:<br class="">><br class="">> 1. return “false” seems to me logically correct, because<br class="">> there is never an empty string in another string, and an empty string cannot contain another empty string, right?<br class=""><br class="">Empty set is a subset of all sets.<br class=""><br class="">Just like:<br class=""><br class="">let arr1: [String] = ["Hello", "Swift", "Evolution"]<br class="">let arr2: [String] = []<br class="">arr1.starts(with: arr2, isEquivalent: ==) // true<br class=""><br class="">> This has worked very conveniently for NSString in ObjC for more than 20 years, why change it?<br class="">> Do you know of cases that were problematic with this convention?<br class="">><br class="">><br class="">> 2 throw a runtime error when trying to do this:<br class="">> str.hasPrefix(“”) // also for hasSuffix, str.contains etc.<br class="">><br class="">> some in-line questions below.<br class="">><br class="">> Kind Regards<br class="">><br class="">> Ted<br class="">><br class="">><br class="">> On 19.07.2016, at 16:31, Dave Abrahams <<a href="mailto:dabrahams@apple.com" target="_blank" class="">dabrahams@apple.com</a>> wrote:<br class="">>><br class="">>><br class="">>> on Tue Jul 19 2016, "Ted F.A. van Gaalen" <<a href="http://tedvgiosdev-at-gmail.com/" target="_blank" class="">tedvgiosdev-AT-gmail.com</a>> wrote:<br class="">>><br class="">>>> Hi Dave<br class="">>>><br class="">>>> “true” ? am I going nuts ? :o)<br class="">>>><br class="">>>> var str = "Hello, playground"<br class="">>>><br class="">>>> print( str.hasPrefix("”)) // case 1 : false<br class="">>>><br class="">>>> print( str.hasSuffix("”)) // case 2 : false<br class="">>>><br class="">>>> print("" == “a” ) // case 3 : false<br class="">>>><br class="">>>> Currently, all cases above evaluate to “false”<br class="">>>> i think that is correct,<br class="">>><br class="">>> I don't know what to tell you. It may seem intuitively correct to you,<br class="">>> but others in the thread have laid out the reasons why it is not<br class="">>> mathematically correct behavior.<br class="">> Where? I couldn’t find any.<br class="">>> One other way of rephrasing it: to get<br class="">>> `false` for str.hasPrefix(""), you actually need special-case code in<br class="">>> hasPrefix to check for the empty string,<br class="">> again, maybe it should throw a run-time error instead.<br class="">><br class="">><br class="">>> and the caller may well also<br class="">>> need special-case code to handle the fact that the result is not<br class="">>> mathematically consistent with other cases on the continuum.<br class="">> In this context as “continuum” :<br class="">> are you referring to “sets” or “collections” here?<br class="">> what other cases?<br class="">><br class="">>> Doing<br class="">>> things that way doesn't work in practice for real programs.<br class="">> please explain thank you, because I see no problems at<br class="">> all with the current NSString-like evaluation…<br class="">> I’d put an s.isEmpty() in front of it.<br class="">>><br class="">>>> because:<br class="">>>><br class="">>>> How can an empty string be a prefix or suffix value?<br class="">>>> as there is no empty string present in a non-empty string.<br class="">>>><br class="">>>> Note that if case 1 and case 2 would evaluate to “true”,<br class="">>>> it would conflict with case 3.<br class="">>>><br class="">>>> Can’t imagine that case 3 should in future also result in “true”<br class="">>>><br class="">>>> ??<br class="">>>><br class="">>>> -----<br class="">>>><br class="">>>> Also I hope that changes to String functionality<br class="">>>> for Swift 4 are not backward breaking changes<br class="">>>> even the more for string handling, because Strings<br class="">>>> are heavily used in most apps.<br class="">>>><br class="">>>> I am firmly convinced that all future releases of Swift<br class="">>>> should compile Swift 3 and higher source files without<br class="">>>> any changes 100 % flawlessly! This prevents early diminishing<br class="">>>> of Swift’s popularity, especially with those building large<br class="">>>> codebases using Swift.<br class="">>>><br class="">>>> I’ve started a thread about this a week ago,<br class="">>>> however no one found this important enough to<br class="">>>> share their opinions with me yet, or were too busy with<br class="">>>> other subjects to do so.<br class="">>>><br class="">>>> Increasingly I have dreams, me<br class="">>>> programming complete apps in Smalltalk<br class="">>>> and then automagically generate<br class="">>>> an macOS, tvOS or iOS runtime app of it.<br class="">>>><br class="">>>> (I have also dreams of this world becoming<br class="">>>> a nice and peaceful placebut that is<br class="">>>> beyond the context of this forum)<br class="">>>><br class="">>>> Kind Regards<br class="">>>> TedvG<br class="">>>><br class="">>>><span class="Apple-converted-space"> </span><a href="http://www.speyer.de/" rel="noreferrer" target="_blank" class="">www.speyer.de</a><br class="">>>><br class="">>>>> on Mon Jul 18 2016, Kevin Nattinger <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a><span class="Apple-converted-space"> </span><mailto:<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>>> wrote:<br class="">>>>><br class="">>>>>> I agree, true is definitely the expected behavior. In particular, it<br class="">>>>>> seems absurd to me that `a.hasPrefix(b)` and `a.hasSuffix(b)` could be<br class="">>>>>> false when `a == b` is true.<br class="">>>>><br class="">>>>> I expect to be reworking Strings for Swift 4, and this is one of the<br class="">>>>> many things we plan to address.<br class="">>>>><br class="">>>>> --<br class="">>>>> Dave<br class="">>>>><br class="">>>>><br class="">>>><br class="">>><br class="">>> --<br class="">>> Dave<br class="">><br class="">> _______________________________________________<br class="">> swift-evolution mailing list<br class="">><span class="Apple-converted-space"> </span><a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a><br class="">><span class="Apple-converted-space"> </span><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""><br class="">_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""></blockquote></div></div></div><div dir="ltr" class="">--<span class="Apple-converted-space"> </span><br class=""></div><div data-smartmail="gmail_signature" class="">Bianca<br class=""><a href="http://biancatamayo.me/" target="_blank" class="">http://biancatamayo.me</a></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" target="_blank" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""></div></blockquote></div><br class=""></div></div></div></div><br class="">_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""><br class=""></blockquote></div><br class=""></div></div></div></blockquote></div><br class=""></div></div></div></div><br class="">_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a></blockquote></div></div></div></div></blockquote></div><br class=""></body></html>