<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 class=""><h3 class="" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.43; font-size: 1.5em; 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);">Properties with initial values</h3><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; line-height: 25px; background-color: rgb(255, 255, 255);"><pre class="" 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;"><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">struct</span> S {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> s: <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);">=</span> <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>hello<span class="pl-pds" style="box-sizing: border-box;">"</span></span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> i: <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);">42</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">// user declares:</span>
memberwise <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>() {}
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">// compiler synthesizes:</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>(s: <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);">=</span> <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>hello<span class="pl-pds" style="box-sizing: border-box;">"</span></span>, i: <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);">42</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>s <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> s
<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>i <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> i
}
}</pre></div></div><div class=""><br class=""></div><div class="">I think the sticking issue here is that this synthesis isn't congruent with the current rules around let:</div><div class=""><br class=""></div><div class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(187, 44, 162);" class="">struct<span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> S {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">let</span> s: <span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">String</span> = <span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">"hello"</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">let</span> i: <span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Int</span> = <span style="font-variant-ligatures: no-common-ligatures; color: #272ad8" class="">42</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=""><span class="Apple-tab-span" style="white-space:pre"> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">init</span>(s: <span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">String</span> = <span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">"hello"</span>, i: <span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Int</span> = <span style="font-variant-ligatures: no-common-ligatures; color: #272ad8" class="">42</span>) {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span>.<span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">s</span> = s</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span>.<span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">i</span> = i</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(0, 132, 0);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span>//note: initial value already provided in 'let' declaration</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(0, 132, 0);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span>//note: change 'let' to 'var' to make it mutable</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>}</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">}</div></div><div class=""><br class=""></div><div class=""><div class=""><i class="">4) var properties with default initializers should have their parameter to the synthesized initializer defaulted.</i></div><div class=""><br class=""></div><div class="">I don't think anyone would have issue with this:</div><br class="Apple-interchange-newline"><pre class="" style="color: rgb(51, 51, 51); 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;"><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">struct</span> S {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> s: <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);">=</span> <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>hello<span class="pl-pds" style="box-sizing: border-box;">"</span></span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> i: <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);">42</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">// user declares:</span>
memberwise <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>() {}
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">// compiler synthesizes:</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>(s: <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);">=</span> <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>hello<span class="pl-pds" style="box-sizing: border-box;">"</span></span>, i: <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);">42</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>s <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> s
<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>i <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> i
}
}</pre><div class=""><br class=""></div></div><div class=""><br class=""></div><br class=""><div><blockquote type="cite" class=""><div class="">On Dec 22, 2015, at 1:02 PM, Matthew Johnson 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=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Dec 22, 2015, at 12:51 PM, Guillaume Lessard 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="">Hi,<br class=""><br class="">Regardless of anything else in the proposal, I strongly dislike its attempted subversion of `let` properties.<br class=""><br class="">struct A {<br class=""> let member = 1 // It’s done, over. If that’s not what you want, don’t initialize it here.<br class="">}<br class=""><br class=""></div></blockquote><div class=""><br class=""></div><div class="">This is not an attempt to subvert `let` properties. The `= 1` in the declaration can <i class="">very reasonably</i> be viewed as a default value that should be used if the member is not otherwise initialized.</div><div class=""><br class=""></div><div class="">Why would you have an immutable instance member that is always going to have a constant value of 1? That just wastes space by duplicating the constant value in many instances. However it is quite reasonable to have an immutable instance member that <b class="">defaults </b>to 1, but may have a different value depending on the initializer that is used for the instance.</div><div class=""><br class=""></div><div class="">Matthew</div></div>
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