<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=""><br class=""><div><blockquote type="cite" class=""><div class="">On Dec 11, 2015, at 11:50 PM, Chris Lattner via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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; float: none; display: inline !important;" class="">Hi Amir,</span><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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;">Please read up on the semantics of for-in loops & generators, and if you think this is a good idea, then propose the actual language changes necessary to provide this behavior. Thanks,</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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;">-Chris</div></div></blockquote><br class=""></div><div>An 'inout' for loop would be handy for some use cases, but would probably depend on a MutableCollectionType at minimum rather than any arbitrary SequenceType. You can implement a mutable version of 'forEach' as a higher-order function extension on MutableCollectionType today:</div><div><br class=""></div><div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(112, 61, 170);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">extension</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span>MutableCollectionType<span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">mutating</span> <span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">func</span> mutableForEach(body: (<span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">inout</span> Generator.Element) <span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">throws</span> -> ()) <span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">rethrows</span> {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">for</span> index <span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">in</span> indices {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">try</span> body(&<span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span>[index])</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> }</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> }</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">}</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">var</span> x = [<span style="font-variant-ligatures: no-common-ligatures; color: #272ad8" class="">1</span>,<span style="font-variant-ligatures: no-common-ligatures; color: #272ad8" class="">2</span>,<span style="font-variant-ligatures: no-common-ligatures; color: #272ad8" class="">3</span>]</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">x.mutableForEach { (<span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">inout</span> y: <span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Int</span>) <span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">in</span> y += <span style="font-variant-ligatures: no-common-ligatures; color: #272ad8" class="">1</span> }</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">print(x)</div><div class=""><br class=""></div><div class="">If you want to propose this as a language feature, you could use a library implementation like this as a starting point for proposing how it would work.</div><div class=""><br class=""></div><div class="">-Joe</div></div></body></html>