<html><head><style>body{font-family:Helvetica,Arial;font-size:13px}</style></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><div id="bloop_customfont" style="margin: 0px;">> How so? It seems that encapsulation is orthogonal to reference/value semantics.</div><div id="bloop_customfont" style="margin: 0px;"><br></div><div id="bloop_customfont" style="margin: 0px;">Consider this type</div><div id="bloop_customfont" style="margin: 0px;"><br></div><div id="bloop_customfont" style="margin: 0px;">public struct Mailbox {</div><div id="bloop_customfont" style="margin: 0px;"> private var _messages: [String]</div><div id="bloop_customfont" style="margin: 0px;"> public mutating func append(message: String) { _messages.append(message)}</div><div id="bloop_customfont" style="margin: 0px;"> public var messages: [String] { return _messages}</div><div id="bloop_customfont" style="margin: 0px;"> public var sortedMessages: [String] { return _messages.sorted() }</div><div id="bloop_customfont" style="margin: 0px;">}</div><div id="bloop_customfont" style="margin: 0px;"><br></div><div id="bloop_customfont" style="margin: 0px;">We subsequently discover in the wild that although there are a variety of client patterns, certain "important" clients have the particular pattern</div><div id="bloop_customfont" style="margin: 0px;"><br></div><div id="bloop_customfont" style="margin: 0px;">1. Add messages up front</div><div id="bloop_customfont" style="margin: 0px;">2. Use sortedMessages accessor frequently and exclusively</div><div id="bloop_customfont" style="margin: 0px;"><br></div><div id="bloop_customfont" style="margin: 0px;">It would improve the important clients without harming other clients to use the following implementation for our type: if the sorted accessor is used before the unsorted one, sort the underlying storage, and then serve that until the type is subsequently mutated (which important clients do not do). This amortizes the cost of the sort across many calls to the accessor.</div><div id="bloop_customfont" style="margin: 0px;"><br></div><div id="bloop_customfont" style="margin: 0px;">Although the underlying storage is "private" and we may consider its sorted-arity an implementation detail of Mailbox, in fact there is no straightforward way to get to that implementation from this one. When we chose value semantics we promised clients that our "encapsulated" values will not change inside a getter; mutating the "hidden" storage breaks our promise.</div><div id="bloop_customfont" style="margin: 0px;"><br></div><div id="bloop_customfont" style="margin: 0px;">I would argue this "encapsulation failure" of the _messages array is actually a feature, and part of the draw of value types is that they provide these kinds of guarantees to clients, and we subvert them at our peril. In cases where that is not desired reference types are available.</div><div id="bloop_customfont" style="margin: 0px;"><br></div><div id="bloop_customfont" style="margin: 0px;">> We want to be able to add new stored properties to structs, or change existing stored properties to computed properties (and vice versa) without breaking binary or source compatibility.</div><div id="bloop_customfont" style="margin: 0px;"><br></div><div id="bloop_customfont" style="margin: 0px;">If CGAffineTransform, CGPoint, in_addr_t etc. are changing their members we have a problem. There are probably structs where this makes more sense, but I can't immediately think of an example.</div></div> <br> <div id="bloop_sign_1511237234042792960" class="bloop_sign"></div> <br><p class="airmail_on">On November 20, 2017 at 6:16:55 PM, Slava Pestov (<a href="mailto:spestov@apple.com">spestov@apple.com</a>) wrote:</p> <blockquote type="cite" class="clean_bq"><span><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div></div><div>
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<div class="">On Nov 20, 2017, at 1:58 PM, Drew Crawford 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="">
<div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; margin: 0px;" class="">I'm "weak oppose" on this proposal.</div>
<div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; margin: 0px;" class=""><br class=""></div>
<div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; margin: 0px;" class="">The core premise here is to increase the encapsulation of
a struct around its member variables. But I think the purview
of encapsulation is more classes than structs.</div>
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How so? It seems that encapsulation is orthogonal to
reference/value semantics.</div>
<div><br class="">
<blockquote type="cite" class="">
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<div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; margin: 0px;" class=""> e.g. a struct leaks information about the mutation
of its member variables, even if those variables are private.</div>
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<div>Can you explain what you mean by this?</div>
</div>
<div><br class="">
<blockquote type="cite" class="">
<div class="">
<div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; margin: 0px;" class=""> Structs are the obvious implementation for a named
tuple (CGPoint CGAffineTransform UIColor etc.) where there is
inherently a fixed set of members that are more conveniently
accessed directly. Structs and classes have different
purposes and so the argument for consistency with classes is
weak.</div>
<div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; margin: 0px;" class=""><br class=""></div>
<div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; margin: 0px;" class="">With regard to the BalancedPair problem, I would prefer to
see a "final struct" or "required init”.</div>
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</blockquote>
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<div>The real reason we want to introduce this language change is
to solve some problems related to resilience. We want to be able to
add new stored properties to structs, or change existing stored
properties to computed properties (and vice versa) without breaking
binary or source compatibility. Since non-delegating initializers
expose the exact set of stored properties to the client module,
they break the encapsulation that we need to allow this.</div>
<div><br class=""></div>
Slava<br class="">
<blockquote type="cite" class="">
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<p class="airmail_on" style="font-family: Helvetica, Arial; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">
On November 14, 2017 at 1:31:25 PM, Ted Kremenek (<a href="mailto:kremenek@apple.com" class="">kremenek@apple.com</a>)
wrote:</p>
<blockquote type="cite" class="clean_bq" style="font-family: Helvetica, Arial; font-size: 13px; 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-size-adjust: auto; -webkit-text-stroke-width: 0px;">
<div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">
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<p class="" style="-webkit-print-color-adjust: exact; margin-right: 0px; margin-bottom: 15px; margin-left: 0px; font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255); margin-top: 0px !important;">
<span class="">The review of "SE-0189: Restrict Cross-module Struct
Initializers" begins now and runs through <strong class="" style="-webkit-print-color-adjust: exact;">November 21,
2017</strong>.</span></p>
<p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">
<span class="">The proposal is available here:</span></p>
<blockquote class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; border-left-width: 4px; border-left-style: solid; border-left-color: rgb(221, 221, 221); padding: 0px 15px; color: rgb(119, 119, 119); font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">
<div class="" style="-webkit-print-color-adjust: exact; margin: 0px;"><span class=""><a href="https://github.com/apple/swift-evolution/blob/master/proposals/0189-restrict-cross-module-struct-initializers.md" class="">https://github.com/apple/swift-evolution/blob/master/proposals/0189-restrict-cross-module-struct-initializers.md</a></span></div>
</blockquote>
<p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">
<span class="">Reviews are an important part of the Swift evolution
process. All review feedback should be sent to the swift-evolution
mailing list at:</span></p>
<blockquote class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; border-left-width: 4px; border-left-style: solid; border-left-color: rgb(221, 221, 221); padding: 0px 15px; color: rgb(119, 119, 119); font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">
<div class="" style="-webkit-print-color-adjust: exact; margin: 0px;"><span class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span></div>
</blockquote>
<p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">
<span class="">or, if you would like to keep your feedback private,
directly to the review manager. </span></p>
<p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">
<span class="">When replying, please try to keep the proposal link
at the top of the message:</span></p>
<blockquote class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; border-left-width: 4px; border-left-style: solid; border-left-color: rgb(221, 221, 221); padding: 0px 15px; color: rgb(119, 119, 119); font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">
<div class="" style="-webkit-print-color-adjust: exact; margin: 0px;"><span class="">Proposal link:<span class="Apple-converted-space"> </span><a href="https://github.com/apple/swift-evolution/blob/master/proposals/0189-restrict-cross-module-struct-initializers.md" class="">https://github.com/apple/swift-evolution/blob/master/proposals/0189-restrict-cross-module-struct-initializers.md</a><br class="" style="-webkit-print-color-adjust: exact;">
...<br class="" style="-webkit-print-color-adjust: exact;">
Reply text<br class="" style="-webkit-print-color-adjust: exact;">
...<br class="" style="-webkit-print-color-adjust: exact;">
Other replies</span></div>
</blockquote>
<h3 id="toc_0" class="" style="-webkit-print-color-adjust: exact; margin: 20px 0px 10px; padding: 0px; -webkit-font-smoothing: antialiased; cursor: text; position: relative; font-size: 18px; font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">
What goes into a review of a proposal?</h3>
<p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">
The goal of the review process is to improve the proposal under
review through constructive criticism and, eventually, determine
the direction of Swift. </p>
<p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">
When reviewing a proposal, here are some questions to consider:</p>
<ul class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; padding-left: 30px; font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">
<li class="" style="-webkit-print-color-adjust: exact; margin: 0px;">
<p class="" style="-webkit-print-color-adjust: exact; margin: 0px 0px 15px;">What is
your evaluation of the proposal?</p>
</li>
<li class="" style="-webkit-print-color-adjust: exact; margin: 0px;">
<p class="" style="-webkit-print-color-adjust: exact; margin: 0px 0px 15px;">Is the
problem being addressed significant enough to warrant a change to
Swift?</p>
</li>
<li class="" style="-webkit-print-color-adjust: exact; margin: 0px;">
<p class="" style="-webkit-print-color-adjust: exact; margin: 0px 0px 15px;">Does
this proposal fit well with the feel and direction of Swift?</p>
</li>
<li class="" style="-webkit-print-color-adjust: exact; margin: 0px;">
<p class="" style="-webkit-print-color-adjust: exact; margin: 0px 0px 15px;">If you
have used other languages or libraries with a similar feature, how
do you feel that this proposal compares to those?</p>
</li>
<li class="" style="-webkit-print-color-adjust: exact; margin: 0px;">
<p class="" style="-webkit-print-color-adjust: exact; margin: 0px 0px 15px;">How much
effort did you put into your review? A glance, a quick reading, or
an in-depth study?</p>
</li>
</ul>
<p class="" style="-webkit-print-color-adjust: exact; margin-top: 15px; margin-right: 0px; margin-left: 0px; font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255); margin-bottom: 0px !important;">
Thanks,<br class="" style="-webkit-print-color-adjust: exact;">
Ted Kremenek<br class="" style="-webkit-print-color-adjust: exact;">
Review Manager</p>
_______________________________________________<br class="">
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https://lists.swift.org/mailman/listinfo/swift-evolution-announce<br class="">
</div>
</div>
</blockquote>
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