<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Currently possible to add extension to class, so we can separate the implementation to different class files. In some situation this still have some limitations, <div class="">For example: </div><div class=""><br class=""></div><div class=""><pre style="box-sizing: border-box; overflow: auto; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal; color: rgb(51, 51, 51);" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">class</span> Racer {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> name:<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">String</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>(name:<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">String</span>) {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">self</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>name <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> name
}
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">extension</span> Racer {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> winTimes:<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);">// requires access local variable</span>
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</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);">win</span>() {
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">// need to update local variable</span>
}
}</pre><div class=""><br class=""></div></div><div class="">the method in the extension sometimes need add another variable to store values, if you are extending the system class, that will be very hard to make this happen</div><div class=""><br class=""></div><div class="">So I am thinking, can we add another namespace ˇ°externalˇ± besides ˇ°public, private, internalˇ±, with this we can define a ˇ°external varˇ± inside the extension scope.</div><div class="">the variable needs a default value, and only can accessed in the extension scope, the implementation for the example will like this: </div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; 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);"><pre style="box-sizing: border-box; overflow: auto; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">class</span> Racer {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> name:<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">String</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>(name:<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">String</span>) {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">self</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>name <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> name
}
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">extension</span> Racer {
external <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> _winTimes:<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span> <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);">0</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> winTimes:<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> _winTimes
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</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);">win</span>() {
_winTimes<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">++</span>
}
}</pre></div><h2 style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); 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'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-impact-on-existing-code" class="anchor" href="https://github.com/chenyunguiMilook/swift-evolution#impact-on-existing-code" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1;"><span class="octicon octicon-link" style="box-sizing: border-box; font-weight: normal; font-size: 16px; line-height: 1; font-family: octicons; display: inline-block; text-rendering: auto; -webkit-font-smoothing: antialiased; -webkit-user-select: none; color: rgb(0, 0, 0); vertical-align: middle; visibility: hidden;"></span></a></h2></div><div class=""> </div></body></html>