<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="">Proposal Link: <a href="https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md" class="">https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md</a><div class=""><br class=""></div><div class="">Hello Swift Community,</div><div class=""><br class=""></div><div class="">The review of SE-0169 "Improve Interaction Between `private` Declarations and Extensions” ran from April 6...11, 2017. The proposal is <b class="">accepted</b>.</div><div class=""><br class=""></div><div class="">This topic has been highly controversial for a long time, both during Swift 3’s development (when <a href="https://github.com/apple/swift-evolution/blob/master/proposals/0025-scoped-access-level.md" class="">SE-0025</a> was introduced) and during Swift 4 (including <a href="https://github.com/apple/swift-evolution/blob/master/proposals/0159-fix-private-access-levels.md" class="">SE-0159</a> and <a href="https://github.com/apple/swift-evolution/pull/680" class="">other</a> <a href="https://github.com/apple/swift-evolution/pull/681" class="">proposals</a>). There is no solution that will make everyone happy: maintaining the status quo makes “fileprivate” too common and therefore not meaningful when it occurs in source; removing or diluting scope-level access control (as in <a href="https://github.com/apple/swift-evolution/blob/master/proposals/0159-fix-private-access-levels.md" class="">SE-0159</a> and this proposal) takes away a tool that is in use by Swift developers; and adding more levels of access control complicates the language.</div><div class=""><br class=""></div><div class="">The core team feels that this proposal makes <font face="Menlo" class="">private</font> access align more closely with the goals of the language:</div><div class=""><br class=""></div><div class=""><ul class="MailOutline"><li class="">It supports the notion that extensions are a code-organization tool: one should be able to break up a type’s definition into several extensions to improve the clarity of that code, without having to open up access or otherwise view the members in different extensions as completely-distinct entities. The core team expects future language evolution to reinforce the notion that extensions are more of a code organization tool than distinct entities, e.g., allowing stored properties to be introduced in an extension.</li><li class="">It makes <font face="Menlo" class="">private</font> more usable as the default sub-<font face="Menlo" class="">internal</font> access level, which supports progressive disclosure of the access control system and better matches with programmer’s expectations about what <font face="Menlo" class="">private</font> access means.</li><li class="">It makes <font face="Menlo" class="">fileprivate</font> more meaningful, because it is only needed for those cases where one is reaching across types (or among types and globals) within a file. It will also become more rare, which matches well with its longer, descriptive name.</li></ul><div class=""><br class=""></div></div><div class="">The proposal’s acceptance includes one modification: extensions of a given type that reside in a single file that is different from the file that defines the type itself will have access to the <font face="Menlo" class="">private</font> members of all other extensions in that file. For example:</div><div class=""><br class=""></div><div class=""><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal; color: rgb(36, 41, 46);" class=""><span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> FileA.swift</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">struct</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">A</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">private</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> aMember <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>
}
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> FileB.swift</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">extension</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">A</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">private</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">foo</span>() {
<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">bar</span>() <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> ok, foo() does have access to bar()</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> }
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">extension</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">A</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">private</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">bar</span>() {
aMember <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">42</span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> not ok, private members may not be accessed outside their file.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> }
}</pre><div class=""><br class=""></div></div><div class="">The proposal has already been updated to reflect this change, which better reflects the notion that extensions are a code-organization tool.</div><div class=""><br class=""></div><div class="">The core team considers the access-control matter closed for Swift 4 and will not be reviewing any further proposals in this area.</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- Doug</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>Review Manager</div></body></html>